What is the sum of the geometric series in which a1 = −5, r = 3, and an = −405? 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. (1 point) Sn = −605 Sn = −1,220 Sn = −15 Sn = 605