Question 1101665
A, the first term
The 15th term is  {{{A+14d=129}}}.
Sum of first 15 terms is {{{(15/2)(2A+14d)=1095}}}.
Two linear equations in A and d.


A simplified system of equations: {{{system(A+14d=129,A+7d=73)}}}.



{{{system(d=8,A=17)}}}


Sum of first ten terms?  {{{(10/2)(17+(17+(10-1)*8))}}}
Simplify and compute.