find sum to n terms (8\5) + (16\65) + (24\325)+............

it is in the form of

8/5 + 2*8/5*13  + 3*8/5*5*13 +....

take 8 as a common term

8(  1/5  +  2/5*13  + 3/5*5*13......

take 1/13 as common term from second

8(  1/5  +  1/13(  2/5 +  3/5*5  +  4/5*5*5.....

the term in braces is AGP as  1 +2a + 3a*a +4*a*a*a... =1/(1-a)^2