The real numbers is one set, and so is the the set of integers since this set is { ..., -3, -2, -1, 0, 1, 2, 3, ...} composed of positive and negative whole numbers, along with 0.
The value -15 is also in the rational set because we can write it as a fraction of two integers: -15 = -15/1
The 3 answers are: real numbers, integers, rational numbers