Geometric Series Help! Algebra 2!?

Question

I need help solving these types of geometric series questions. all they give me is..
A1= -4 r= 4 and Sn= -5460
they tell me to find n.
i have to use the formula
Sn=A1(1-r^n) over 1-r

Answer 1

Given that A₁ = - 4, r = 4, Sn = - 5460

Substitute A₁ = - 4, r = 4, Sn = - 5460 in the equation

Multiply each side by negative one

Divide each side by 4

Multiply each side by -3

Subtract 1 from each side

Multiply each side by negative one

Therefore n = 6.