What comes next in the sequence: 105, 99, 90, 81, ??

Answer 1

105 => 1 + 0 + 5 = 6
105 - 6 = 99
99 => 9 + 9 = 18 => 1 + 8 = 9
99 - 9 = 81
Similarly
81 - 9 = 72
The series ends with 0.

Answer 2

It follows below logic
105 - 6 = 99 1+0+5 = 6
99 - 9 = 90 9 + 9 = 18 18 = 1 + 8 = 9
90 - 9 = 81 9 + 0 = 9
81 - ? = ? 8 + 1 = 9
Then, 81 - 9 = 72