derivatives and limits

A manufacturer has the following data on the variation of its prices in relation to the quantity demanded: at a unit price of $ 78.00, the quantity demanded is 1200 units. With a 36% increase in price, the quantity demanded drops to 28,08 units. To determine:

a) The amount that must be needed for a recipe to be maximum, a recipe maximum and the unit price.

b) Determine in which quantity sold intervals the revenue is increasing and decreasing.