Answer
$\displaystyle \sum_{i=1}^{5}3^{i-1}=121$
Work Step by Step
$\displaystyle \sum_{i=1}^{5}3^{i-1}=3^0+3^1+...+3^4$
$a_1=3^0=1$
$r=\frac{a_2}{a_1}=\frac{3^1}{3^0}=3$
$S_n=a_1(\frac{1-r^n}{1-r})$
$S_5=1(\frac{1-3^5}{1-3})=\frac{1-243}{-2}=121$
