#### Answer

$a_{5}=a_{1}\times r^{4}=-2\times \left( -3\right) ^{4}=-162;$
$a_{n}=a_{1}\times r^{n-1}=-2\times \left( -3\right) ^{n-1}$

#### Work Step by Step

$r=\dfrac {54}{-18}=\dfrac {-18}{6}=\dfrac {6}{-2}=-3;a_{1}=-2\Rightarrow a_{5}=a_{1}\times r^{4}=-2\times \left( -3\right) ^{4}=-162;a_{n}=a_{1}\times r^{n-1}=-2\times \left( -3\right) ^{n-1}$