72, 9, 82, 10, 88, 16, 86, 14, 99, ?

In this type of number series, each number is paired with a value equal to the sum of its own digits. Spotting this digit-sum relationship between consecutive terms is the key to extending the sequence.

1. Group the sequence into (number, paired value) pairs: (72, 9), (82, 10), (88, 16), (86, 14), (99, ?).

2. Check the digit sum of each number against its paired value: 7 + 2 = 9, matches; 8 + 2 = 10, matches; 8 + 8 = 16, matches; 8 + 6 = 14, matches.

3. Apply the same digit-sum rule to the last number, 99: 9 + 9 = 18.

The digit-sum relationship holds consistently across all four given pairs before being extended to 99, confirming 18 as the correct next term.