The accompanying graph represents Hayden's Fro$-$Yo Emporium, which is the only seller of frozen yogurt in a small college town, showing the marginal cost $($MC$),$ average cost $($AC$),$ marginal revenue $($MR$),$ and demand $($D$)$ curves.

How many cups of frozen yogurt should Hayden sell?

$q_2$

$q_3$

$q_4$

$q_1$

Quantity $($cups of frozen yogurt$)$

How much should Hayden charge per cup?

$p_4$