Repeat example $3$ if she wants the weekly revenue to be $$4,200.$

Example $3$ A manufacturer of hard shell cases for the iPhone knows that the number of cases she can sell each week is related to the price of the cases by the equation $x=1,300-100p,$ where $x$ is the number of cases and $p$ is the price per case. What price should she charge for each case if she wants the weekly revenue to be $$4,000?$

$($Make sure you are using $4200$ instead of $4000)$