This is an increasing sequence, with -9 as its first term. The first increase is +3, then +5, +7, and +9. The differences increase by 2 each time. The sixth term will be 15 + 11, and the seventh would be 15 + 11 + 13. We can follow this pattern to get to the tenth term. 15 + 11 + 13 + 15 + 17 + 19 = 90
