No Explaination.

Let R be the set of all real numbers.
Consider the following subsets of the plane R x R:

S = {(x, y) : y = x + 1 and 0 < x
< 2} and T = {(x, y) : x -
y is an integer }

If two sets A and B have 17 elements in common, then the number of elements common to the set A x B and B x A is