Hey. Well, to answer this question, it is simply reversing the processes to find out what f is equal to. Essentially, you want to get f all by itself so we can find out what it is.
92 = 8(f+2)-4
92+4 = 8(f+2) ------ (Add 4 to both sides.)
96 = 8(f+2) ------- (ONE STEP CLOSER! Now, divide both sides by 8)
12 = f+2 ------(Looking good. Go on and subtract 2 from both sides.)
f = 10
Super cool. It's just to reverse whatever is done on the other side. If 2 is added on one side, go on and subtract it!
If you want to check, just go on and plug 10 into f in the original equation. It comes to 92!