the sum of the first 8 terms of an Approval ia 12 and the the sum of the first 16 term is 56.find the first 3 terms3 of the Ap

Answer 1

No ideas?
8/2 (2a+11d) = 12
16/2 (2a+15d) = 56
Solve for a and d, and then get
S3 = 3/2 (2a+2d)

Answer 2

a=-4 and d=1