Answer
$a_{5}=a_{1}\times r^{5-1}=\dfrac {9}{4}\times 2^{4}=36;$
$a_{n}=a_{1}\times r^{n-1}=\dfrac {9}{4}\times 2^{n-1}$
Work Step by Step
$a_{1}=\dfrac {a_{4}}{r^{3}}=\dfrac {18}{2^{3}}=\dfrac {9}{4};a_{5}=a_{1}\times r^{5-1}=\dfrac {9}{4}\times 2^{4}=36;a_{n}=a_{1}\times r^{n-1}=\dfrac {9}{4}\times 2^{n-1}$
