According to economic theory, the supply A: of a quantity in a free market increases as the

Question:

According to economic theory, the supply A: of a quantity in a free market increases as the price p increases (see the figure).

Suppose that the number x of DVD players a retail chain is willing to sell per week at a price of $p is given by

(A) Find dx/dp.
(B) Find the supply and the instantaneous rate of change of supply with respect to price when the price is $40. Write a brief verbal interpretation of these results.
(C) Use the results from part (B) to estimate the supply if the price is increased to $41.