The total revenue R earned (in dollars) from producing a gift box of tea is given by

Question:

The total revenue R earned (in dollars) from producing a gift box of tea is given by
R (p) = −10p2 + 800p where p is the price per box (in dollars).
(a) Find the revenues when the prices per box are $20, $25, and $30.
(b) Find the unit price that yields a maximum revenue. What is the maximum revenue? Explain your results.