Assuming you have to solve it for f, you have to rewrite the equation in a form like f = ...
So in the form it is now, you're solving for C. You're not actually going to get values for f or C, for that you'd need more information.
So how do we convert the C = ... form into an f = ... form? Step by step you want to isolate f using simple rules:
step 1) I want to get rid of the 5 so we're dividing left and right by 5:
C/5 = 5(f-32)/(9*5) this simplifies to C/5 = (f-32)/9
step 2) Get rid of the 9 by multiplying by 9 left and right:
9*C/5 = 9*(f-32)/9 simplifies to f-32
step 3) I want to get rid of the -32 so I'm adding 32 left and right:
9*C/5 + 32 = f-32 + 32 simplifies to 9*C/5 + 32 = f
Now just swap left and right, and we get:
f = 9C/5 + 32
All you have to learn is the basic tricks like adding left and right, multiplying left and right. Hope this helps.