Help me out with this, plz!!!?

Question

For every natural number (integer > or = 0) a and b, we have:
f(a*b)=f(a)+f(b)
Find f(1).

Answer 1

Let b = 1. (Or a, but for some reason I prefer b.) Note that this means f(a*1) = f(a) + f(1), or f(a) = f(a) + f(1).

Now subtract f(a) from both sides!

Answer 2

f(1)=f(1*1)=f(1)+f(1) so f(1) = 2f(1) so f(1)=0