Here is the problem:

show that if f:A B and G, H are substes of B, then

(G H) = (G) (H)

and

(G H) = (G) (H)

So I understand the main principle behind an inverse, such that if f(x) H, then x (H). I also understand the proof for inverse composite functions. But this is confusing. How do I prove this?? Thank you