A and b are equal. A represents a multiple of 3+1, and b represents a multiple of 3-1. They represent the same set. The element on the side is divided by 3, and the remainder is 1.

All the elements in C are contained in A, because if a number is divided by 6 and the remainder is 1, then if it is divided by 3, the remainder is also 1, so all the elements in C are in A, but the elements in A are not necessarily in C, such as 4.

So, A = B, A and B contain C, and C is the proper subset of A and B.