A store sells CDs at one price and DVDs at another price. The figure below shows the revenue (in dollars) of the music store as a function of the number, $c$, of CDs and the number, $d$, of DVDs that it sells. The values of the revenue are shown on each line.

(Hint: for this problem there are many possible ways to estimate the requisite values; you should be able to find information from the figure that allows you to give an answer that is essentially exact.)

(a) What is the price of a CD? dollars
(b) What is the price of a DVD? dollars