I am having trouble completing the following Trailhead: Create a formula field that determines the number of days between the end date of a contract and today. This is the formula that I am using:

EndDate - TODAY() 

I keep getting the following error when I check the syntax:  Error: Formula result is data type (Number), incompatible with expected data type (Date).

Hi, 
I am unable to install the Salesforce Adoption Dashboards from the appexchange into my dev org.  I get the following error: