#14 Help
14.
The first term is 3(1) - 4 = -1 and the last is 3(18) - 4 = 50
So....the sum is
[ -1 + 50 ] (18/2) = 49 * 9 = 441
15. The first term is 3(1) - 3 = 0 and the last is 3(10) - 3 = 27
So the sum is [ 0 + 27 ] * (10/ 2) = 27 * 5 = 135