Invariant factor decomposition of $\mathbb{Z}_6 \otimes_{\mathbb{Z}} \mathbb{Z}_9$

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I recall the elementary divisor forms of abelian groups from early chapters but I'm unsure about how to deal with it when it's the tensor of $\mathbb{Z}$-modules. Does anyone have any guidance for this problem?

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In general $$\Bbb Z_n\otimes_{\Bbb Z} A\cong A/nA$$ whenever $A$ is an Abelian group. So, what is $6\Bbb Z_9$?