The number -18 does not belong to the subset of real numbers that consists of positive numbers, as all positive numbers are greater than zero. Additionally, -18 also does not belong to the set of natural numbers (which are typically the positive integers: 1, 2, 3, ...).
To summarize, -18 does not belong to:
- The set of positive real numbers
- The set of natural numbers
If you need a more specific subset, please clarify further!