Hi i need help with this following question. I am not sure on how to approach it.

Define the relation R on $\displaystyle \mathbb{N}$ by $\displaystyle xRy\Leftarrow \Rightarrow x^{2}-y^{2}$ is divisible by 7 $\displaystyle (x,y\in \mathbb{N})$

Prove that R is an equivalence relation on $\displaystyle \mathbb{N}$ and describe the equivalence classes $\displaystyle R_{1}$ and $\displaystyle R_{3}$

Any help is appreichated

thanks

(Happy)