Answer
$p=\$11$
(It is in the given range of $9\leq p\leq 15)$
Work Step by Step
As the elacticity is: $E=-(-4p+33))\times\frac{p}{-2p^2+33p}$
The revenue is maximized where $E=1$
Here,
$(4p-33)\times\frac{p}{-2p^2+33p}=1$
$4p^2-33p=-2p^2+33p$
$4p-33=-2p+33$
$p=\$11$
