I won't do your problem for you.  Instead I'll do one EXACTLY like it
so you can do yours EXACTLY the same way.

I'll do this one instead:

Suppose the set of 14 numbers is {28,B,C,D,E,F,G,H,I,J,K,L,M,N}

Since the average = A,



So we multiply both sides by 14:



We substract 28 from both sides



We add 45 to both sides





We divide both sides by 14:



Answer:  

Now do yours the same way.

Edwin