Two positive integers , p and q are connected by p=q+1 . By using the binomial expansion , show that the expression p^{2n}-2nq-1 can be divided exactly by q^2 for all positive integers n .

I can do this part .

This is the continuation :

hence(2) show that 3^{15}+5 can be divided exactly by 4 .

i am not sure about this part .