How Should I write this Tensor Product?

Question

I want to prove that every element of $M \otimes_R R$ is of the form $m \otimes_R 1$, given that $M$ is a unital $R$-module.

I took $x$ as an element of $M \otimes_R R$ and wrote $x = m \otimes_R r = mr \otimes_R 1$, but I got stuck.

I would appreciate it if you guys could help me understand this and show me how to proceed.

Thanks in advance.