$7.($SLO $1,$ SLO $3)$ Elvis Electronics determines that the demand function for pre$-$paid phones, where r is in dollars, is given by:

D$($x$)=300-$ x

$-$XD$\text{'}($x$)$

Given the formula for elasticity of demand E$($x$)=$

$-,$ find the elasticity when

D$($x$)$

the price is $$99$ and state whether the demand is elastic, inelastic or whether it has unit elasticity.

A$.201$; inelastic B$.201$; elastic

$33$

$.$

$67$; inelastic

D$.67$; elastic