Normal Subgroups and Quotient Groups · Easy problem

Let $\varphi: \mathbb Z_{12} \to \mathbb Z_8$ send $k \mapsto 2k \bmod 8$. By the First Isomorphism Theorem, $\mathbb Z_{12}/\ker\varphi \cong \operatorname{im}\varphi$. What is $|\mathbb Z_{12}/\ker\varphi|$?