in B1
=if(C1="yes",A1,"")

If I am reading your question correctly?

alternate interpretation
in C1
=if(B1=A1,"yes","")

"danielle" wrote:

If A1(max score)=5, B1(actual score) is empty, and C1(not applicable) is empty:
What function do I use if: C1 is yes, then value in B1 is the
same as value in A1