controller:
public class ProjectScenario {
    // To display the list of AQ_LineItem__cS
    public list<AQ_LineItem__c>AQ_lineItemList {set;get;}
    //To get the current opportunityId.
    public Id AQId {set;get;}
    // To get the record Id which is editing in visualforcePage.
    public String rId{get;set;}
    public AQ_LineItem__c  Obj_AQLineItem = new AQ_LineItem__c();
    public AQ_LineItem__c  Obj_AQLineItem1 = new AQ_LineItem__c();
    public ProjectScenario(apexpages.StandardController controller){
        AQId = controller.getId();
        system.debug('AQId===>'+AQId);
        AQ_lineItemList =[select id,PictureUrl__c,Name,AQ_Quantity__c,AQ_NetPrice__c,AQ_SellPrice__c,
                          (select id,Name,AQ_Quantity__c,AQ_NetPrice__c,AQ_SellPrice__c from AQ_SubLineItems__r)
                          from AQ_LineItem__c where Project__c=:AQId];
        system.debug('AQ_lineItemList project'+AQ_lineItemList);
    }
    public void CalculateTotal(){
        Obj_AQLineItem = [select id,AQ_Quantity__c,AQ_NetPrice__c,AQ_SellPrice__c from AQ_LineItem__c  where id =:rId];
        system.debug('Obj_AQLineItem===>'+Obj_AQLineItem.AQ_Quantity__c);
        Obj_AQLineItem1=[select id,AQ_Quantity__c,AQ_NetPrice__c,AQ_SellPrice__c from AQ_LineItem__c where id=:Obj_AQLineItem.Id];
        system.debug('Obj_AQLineItem1===>'+Obj_AQLineItem1.AQ_Quantity__c);
        Obj_AQLineItem1.AQ_SellPrice__c=Obj_AQLineItem1.AQ_Quantity__c*Obj_AQLineItem1.AQ_NetPrice__c;
    }
}

visualforcepage:
<apex:page standardController="opportunity" extensions="ProjectScenario" id="page" sidebar="false" showHeader="false" setup="false">
    <style>
        #customers {
        font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
        border-collapse: collapse;
        width: 100%;
        }
       
        #customers td, #customers th {
        border: 1px solid #ddd;
        padding: 8px;
        }
       
        #customers tr:nth-child(even){background-color: #f2f2f2;}
       
        #customers tr:hover {background-color: #ddd;}
       
        #customers th {
        padding-top: 12px;
        padding-bottom: 12px;
        text-align: left;
        background-color: #4CAF50;
        color: white;
        }
    </style>
    <style>
        #customers1 {
        font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
        border-collapse: collapse;
        width: 100%;
        }
       
        #customers1 td, #customers th {
        border: 1px solid #ddd;
        padding: 8px;
        }
       
        #customers1 tr:nth-child(even){background-color: #f2f2f2;}
       
        #customers1 tr:hover {background-color: #ddd;}
       
        #customers1 th {
        padding-top: 12px;
        padding-bottom: 12px;
        text-align: left;
       
        }
    </style>
    <apex:form id="fm">
        <apex:pageBlock id="pb">
            <table id="customers1">
                <tr>
                    <th style="background-color: #4CAF50;">Name</th>
                    <th>{!opportunity.Name}</th>
                </tr>
                <tr>
                    <th style="background-color: #4CAF50;">Amount</th>
                </tr>
                <tr>
                    <th style="background-color: #4CAF50;">CloseDate</th>
                    <th>{!opportunity.CloseDate}</th>
                </tr>
            </table><br/><br/>
            <table id="customers">
                <tr>
                    <th>Image</th>
                    <th>Name</th>
                    <th>AQ_Quantity__c</th>
                    <th>AQ_NetPrice__c</th>
                    <th>AQ_SellPrice__c</th>
                </tr>
                <apex:repeat value="{!AQ_lineItemList}" var="r" id="pbt">
                    <tr>
                        <td><apex:image id="theImage" value="{!r.PictureUrl__c}" width="55" height="55" alt="Description of image here"/></td>
                        <td><apex:outputField value="{!r.Name}"/></td>
                        <td><apex:inputtext value="{!r.AQ_Quantity__c}">
                            <apex:actionSupport event="onchange" action="{!CalculateTotal}" reRender="pbt">
                                <apex:param name="rId" value="{!r.Id}" assignTo="{!rId}"/>
                            </apex:actionSupport>
                            </apex:inputtext></td>
                        <td><apex:outputField value="{!r.AQ_NetPrice__c}"/></td>
                        <td><apex:outputfield value="{!r.AQ_SellPrice__c}"/></td>
                    </tr>
                    <apex:repeat value="{!r.AQ_SubLineItems__r}"  var="T" id="pbt1">
                        <tr>
                            <td></td>
                            <td><apex:outputField value="{!T.Name}"/></td>
                            <td><apex:inputtext value="{!T.AQ_Quantity__c}"/></td>
                            <td><apex:outputField value="{!T.AQ_NetPrice__c}"/></td>
                            <td><apex:outputField value="{!T.AQ_SellPrice__c}"/></td>
                        </tr>
                    </apex:repeat>
                </apex:repeat>
            </table>
        </apex:pageBlock>
    </apex:form>
</apex:page>

I am not able getting onchange value in the quantity field..I am getting the value which is already in the database..but now i want to get value onchange event..

thanks..