Subtract each terms.
2.7 - 1.5 = 1.2
3.9 - 2.7 = 1.2
From these, we can see that they add 1.2 each time. 8.7 is the last number, so each numbers in the sequence is.
1.5, 2.7, 3.9, 5.1, 6.3, 7.5, 8.7
Add all of these numbers together.
1.5 + 2.7 + 3.9 + 5.1 + 6.3 + 7.5 + 8.7 = 35.7
35.7 is your answer
hope this helps
