In Z define the relation xRy iff x and y have the same tens digit

a.)Show that R is an equivalence relation on Z

b.)Describe the set 3/R

c.)Describe the partition induced by the equivalence relation.

This was a question i had on a test which i got wrong

i started by showing R={(10,10),(10,11),(10,12)....(20,20),(20,21)....( xn,yn),(yn,xn)}

which im not sure is correct. and b and c i just got plain wrong.

Knowing the answer is just to my benefit. I spent a good amount of time on this.