The demand, D. for a new rollerball pen is given by D = 0.006p - 0.3p + 120p, where p is the price in dollars. a) Find the rate of change of quantity with respect to price, dD/dp. b) How many units will consumers want to buy when the price is $25 per unit? c) Find the rate of change at p - 25, and interpret this result. d)Would you expect dD/dp to be positive or negative? dD a) dp b) units (Round to the nearest integer as needed.) c) The number of consumers who wants to buy will by when the price is $ per unit. (Round to the nearest integer as needed.) d) Would you expect dDidp to be positive or negative? negative positive