At a price of x dollars, the demand, in thousands of units, for a certain music player is given by the demand function q = 280 e-0.003x.
a. How many music players will be bought at a price of $260?
b. Graph the demand function for 0 ≤ x ≤ 400.
c. Find the marginal demand, q'(x).
d. Interpret the meaning of the derivative.