Answer: -18 is NOT included in the Natural Numbers, Whole Numbers, or Irrationals. Based on the choices you provided, the answer is IRRATIONALS.
Explanation:
Here are the subsets of the Real Numbers (in order) -
Natural Numbers: 1, 2, 3, .... (does not include -18)
Whole Numbers: 0, 1, 2, 3, ... (does not include -18)
Integers: ... -3, -2, -1, 0, 1, 2, 3, ... (INCLUDES -18)
Rationals: ... Integers and terminating and repeating decimals (INCLUDES -18)
Irrationals: ... non-terminating decimals only (decimals that are not rationals) (does not include -18)