<apex:page standardcontroller="Account" sidebar="false" action="{!showRate}" showheader="false" docType="html-5.0" lightningStylesheets="true">
 <apex:form >
<apex:slds />
  <style>
.star-rating fieldset {
  font-size:0;
  white-space:nowrap; 
  display:inline-block;
  width:250px;
  height:50px;
  overflow:hidden;
  position:relative;
  background:
      url('data:image/svg+xml;utf-8,<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="20px" height="20px" viewBox="0 0 20 20" enable-background="new 0 0 20 20" xml:space="preserve"><polygon fill="#DDDDDD" points="10,0 13.09,6.583 20,7.639 15,12.764 16.18,20 10,16.583 3.82,20 5,12.764 0,7.639 6.91,6.583 "/></svg>');
  background-size: contain;
}

.star-rating input { 
   opacity: 0;
   display:inline-block;
   width: 100%;
   height: 100%; 
   margin:0;
   padding:0;
   z-index: 2;
   position: relative;
}

.star-rating input:hover + label,
.star-rating input:checked + label {
     opacity:1;    
   }

.star-rating label {
   opacity: 0;
   position: absolute;
   left: 0;
   top: 0;
   height: 100%;
   width: 20%;
   z-index: 4;
   background: 
      url('data:image/svg+xml;utf-8,<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="20px" height="20px" viewBox="0 0 20 20" enable-background="new 0 0 20 20" xml:space="preserve"><polygon fill="#FFDF88" points="10,0 13.09,6.583 20,7.639 15,12.764 16.18,20 10,16.583 3.82,20 5,12.764 0,7.639 6.91,6.583 "/></svg>');
   background-size: contain;
 }

.star-rating td ~ td label 
               {
  width: 20%;
  z-index: 8;  
}
.star-rating td ~ td ~ td label 
               {
  width: 30%;
  z-index: 7;  
}
.star-rating td ~ td ~ td ~ td label 
               {
  width: 40%;
  z-index: 6;  
}
 .star-rating td ~ td ~ td ~ td ~ td label
               {
                width: 50%;
         z-index: 5; 
               }
.star-rating td ~ td ~ td ~ td ~ td ~ td label {
  width: 60%;
  z-index: 4;
}
.star-rating td ~ td ~ td ~ td ~ td ~ td ~ td label {
  z-index: 3;
  width: 70%;
}
.star-rating td ~ td ~ td ~ td ~ td ~ td ~ td ~ td label {
  z-index: 2;
  width: 80%;
}
 .star-rating td ~ td ~ td ~ td ~ td ~ td ~ td ~ td ~ td label {
  z-index: 1;
  width: 90%;
} 
.star-rating td ~ td ~ td ~ td ~ td ~ td ~ td ~ td ~ td ~ td label {
  z-index: 0;
  width: 100%;
} 
               
.font
{
 font-size: 19px;
}
</style>
 <apex:selectRadio value="{!fr.RatingScore__c}" layout="lineDirection">
   <apex:actionSupport event="onclick" reRender="form"/>
                       <apex:selectOption itemValue="0.5"></apex:selectOption>
                        <apex:selectOption itemValue="1"></apex:selectOption>
                       <apex:selectOption itemValue="1.5"></apex:selectOption>
                        <apex:selectOption itemValue="2"></apex:selectOption>
                       <apex:selectOption itemValue="2.5"></apex:selectOption>
                        <apex:selectOption itemValue="3"></apex:selectOption>
                       <apex:selectOption itemValue="3.5"></apex:selectOption>
                        <apex:selectOption itemValue="4"></apex:selectOption>
                       <apex:selectOption itemValue="4.5"></apex:selectOption>
                        <apex:selectOption itemValue="5"></apex:selectOption>
  </apex:selectRadio>
</apex:form>
</apex:page>

When I am going to merge two case records using trigger I am getting the following error: Compile Error: Specified type SOBJECT:Case cannot be merged

The triiger code is given below:

trigger CaseMergeTrigger on Case (before delete, after delete, after update) {
 
  for(Case c : Trigger.new) {
  List<Case> ls_Case = new List<Case>{new Case(Subject ='testing'),new Case(Subject ='testing2')};

  //List<Case> lst_Case = [SELECT CaseNumber, Subject FROM Case where Subject =:c.Subject];
insert ls_Case ;
Case masterCase = [SELECT CaseNumber, Subject FROM Case WHERE Subject = 'testing' LIMIT 1];
Case mergeCase = [SELECT CaseNumber, Subject FROM Case WHERE Subject = 'testing2' LIMIT 1];
merge masterCase mergeCase;
}
}

Please suggest where I am going wrong.

Thanks.