Find the sum of sigma notation with infinity

infinity
sigma 3[1/4]^n-1
n=1

can you please explain how to solve this?

This is an infinite geometric series with initial term a = 3 and ratio r = 1/4.

Since |r| = 1/4 < 1, this converges to a/(1 - r) = 3/(1 - 1/4) = 4.

I hope this helps!