Thinking Mathematically (6th Edition)

$54$
To find the fourth term put $n=4$ in the above formula, to get: \begin{align} & {{a}_{4}}={{a}_{1}}{{r}^{4-1}} \\ & =2\cdot {{3}^{3}} \\ & =2\cdot 27 \\ & =54 \end{align} The fourth term of the geometric sequence is$54$.