Pls I need help quickly! Mindy owns 20 pairs of shoes and every week she purchases two more pairs. How long will it take for her closet to have 50 pairs of shoes?

What is the sum of the geometric series in which a1 = 7, r = 3, and an = 1,701? hint: cap s sub n equals start fraction a sub one left parenthesis one minus r to the power of n end power right parenthesis over one minus r end fraction comma r ≠ 1, where a1 is the first term and r is the common ratio