
Arturo O. answered 03/15/20
Experienced Physics Teacher for Physics Tutoring
p = rV / [1 - (1 + r)-n]
Let us take this step by step.
p/(rV) = 1 / [1 - (1 + r)-n]
rV/p = 1 - (1 + r)-n
1 - rV/p = (1 + r)-n
log(1 - rV/p) = -n log(1 + r)
n = -log(1 - rV/p) / log(1 + r)
You can simplify this a little more if you wish. Work with any base for the logs, as long as you use the same base in both logs,