5a. Show that if f maps X into Y and A is a subset of X, B is a subset of Y then
f(f^(-1)(B)) is a subset of B
NB : f^(-1) is the inverse image ( peta invers).
5b. Show that if f maps X onto Y and B is a subset of Y, then
f(f^(-1)(B)) = B
NB : f maps X onto Y = f onto/surjective ( pada)