#### Answer

$${S_5} = 33$$

#### Work Step by Step

$$\eqalign{
& {\text{the sum of the first }}n{\text{ terms of a geometric sequence}}{\text{ is given by}} \cr
& {S_n} = \frac{{{a_1}\left( {{r^n} - 1} \right)}}{{r - 1}},{\text{ where }}r \ne 1 \cr
& {\text{let }}n = 5,\,\,\,{a_1} = 3{\text{ and }}r = - 2 \cr
& {S_5} = \frac{{\left( 3 \right)\left( {{{\left( { - 2} \right)}^5} - 1} \right)}}{{ - 2 - 1}} \cr
& {\text{simplifying}} \cr
& {S_5} = \frac{{\left( 3 \right)\left( { - 33} \right)}}{{ - 3}} \cr
& {S_5} = 33 \cr} $$