can someone help me with this questuon please its fundamnetal to the topic and preventing me understand the topic!!

Thanks

Edgar

if G is a group and n > or equal to 1 define

G(n) = {x element of G : ord (x) = n}

If G is isomorphic to H show that for all n greater than or equal to 1

mod G(n) = mod H(n)

Deduce that C(subscript 3) * C(subscript 3) is not isomorphic to C(subscript 9)

Is it tru that C 3 * C 5 is isomorphic to C15

whats going on here!!?