What is the sum of the geometric series in which a1 = −4, r = 2, and an = −128?

hint: r ≠ 1, where a1 is the first term and r is the common ratio.
sn = 1,020
sn = −252
sn = 43,690
sn = −1,020

Given:
The geometric series is defined by 
a = a₁ = -4
r = 2

The n-th term is

Because the n-th term is -128, therefore
-4(2ⁿ⁻¹) = -128
2ⁿ⁻¹ = 32 = 2⁵
n-1 = 5
n = 6

The sum of the first n terms is


Therefore


-252

I'm pretty sure it's b). i try drawing the functions out and b is the one that stands out or isnt a "line"