Normal Subgroups and Quotient Groups · Medium problem

In $\mathbb Z_{90}$, let $N = \langle 45\rangle$ and $K = \langle 9\rangle$, so $N \le K \le \mathbb Z_{90}$. Using $|\mathbb Z_{90}/K| = \dfrac{|\mathbb Z_{90}/N|}{|K/N|}$ (the Third Isomorphism Theorem relation), compute $|\mathbb Z_{90}/K|$.