Question 1127671
The common ratio r = (x+3)/(x+1) = (x+8)/(x+3)
Solve for x:
x^2 + 6x + 9 = x^2 + 9x + 8
3x = 1
x = 1/3
Therefore r = (1/3 + 3)/(1/3 + 1) = 10/4
The sum of the first n terms of a G.P. = Sn = a1*(1-r^n)/(1-r)
S15 = (4/3)(1-(10/4)^15/(1-(10/4)) = 827841.4