The next number in the given sequence is 24.
To understand how we arrived at this number, let’s break down the pattern:
- The sequence consists of pairs of numbers: (5, 15), (6, 18), (7, 21), (8, ?).
- In each pair, the first number increases by 1: 5, 6, 7, 8.
- The second number in each pair is calculated by multiplying the first number by 3: 5 * 3 = 15, 6 * 3 = 18, 7 * 3 = 21.
- If we follow that same pattern for the next number: 8 * 3 = 24.
Thus, the sequence continues with the next number as 24.