Thedemand, D, for a new rollerball pen is given by D=0.009p*30.4p*2+120p, where p is the price in dollars.

a)

Find the rate of change of quantity with respect toprice, dD/dp.

b)

How many units will consumers want to buy when the price is $25 perunit?

c)

Find the rate of change at p=25, and interpret this result.

d)

Would you expectdD/dp to be positive ornegative?