If $b|a$ and $f$ is a completely multiplicative function, how can I show that $f(a/b) = f(a) / f(b)$?

Question

I know that $f(ab) = f(a)f(b)$ , but I'm not quite sure how to use this information.

Answer 1

$f(a/b)f(b)=f(a)$ from the multiplicative property of the function. Thus, $f(a/b)=f(a)/f(b)$.