Textbook Problem

Let R be the relation of congruence modulo 3. Which of the following equivalence classes are equal? $\left[7\right],\left[-4\right],\left[-6,\right]\left[4\right],\left[27\right],\left[19\right]$

Let R be the relation of congruence modulo 7. Which of the following equivalence are equal? $\left[35\right],\left[-7\right],\left[12\right],\left[0\right],\left[-2\right],\left[17\right]$