Answer
129
Explanation
−3+6−12+24−...
The series is a geometric progression.
The first term (a) = -3
Common ration (r) = 6/-3
= -2
The formula for getting the sum of a geometric progression is
Sum = a(rⁿ - 1)/(r - 1)
= -3(-2⁷ - 1)/(-2 - 1)
= -3(-128-1)/-3
= (-3 × -129)/-3
= -129
