Kindly help me with the following question.

1. Consider the functional equation f(x-y)=f(x)/f(y). If f'(0)=p and f'(5)=q, then f'(-5) is

A. p^2/q B. q/p C.p/q D. q

I tried differentiating the function but then I would have dy/dx in the function which I do not know how to eliminate.