1.6.62 Fields, Groups, Rings

Condition: let \ (\ mathbb {z} [x]- \) Additative group of polynomas with whole coefficients. Consider the subgroup \ (h \) group \ (\ mathbb {z} [x] \) such that in it all polynomes are divided into \ ((x-3) \). Prove that \ (\ mathbb {z} [x] / h \ cong \ mathbb {z} \).