Suppose the demand for a certain item is given by D(p)=-4p2-8p+900, where p represents the price of the item in dollars. a. Find the rate of change of demand with respect to price. b. Find and interpret the rate of change of demand when the price is $13. a. The rate of change of demand with respect to price is (Simplify your answer.) b. Choose the correct answer below and fill in any answer boxes in your choice.. OA. When the price is $13, demand is decreasing at a rate of about OB. When the price is $13, demand is increasing at a rate of about OC. When the price is $13, demand is decreasing at a rate of about OD. When the price is $13, demand is increasing at a rate of about items for each increase in price of $13. items for each increase in price of $13. items for each increase in price of $1. items for each increase in price of $1.