Alright
First, you rearrange it into f(x + 1) = f(x) - x^2, I swapped the order cause it is easier to work with
f(3) = f(2 + 1) = 7
Now from the f(x+1) equation you can say f(2 + 1) = f(2) - 2^2 = 7
f(2) - 4 = 7
so f(2) = 11
f(2) = f(1 + 1) = 11
From the f(x + 1) function again, f(1 + 1) =...