Acompany that manufactures cell phones has done research to determine how the pricing of thier phones affects how many they sell and how much money they make. they have determined that if p is the price of a phone in dollars, the following equations model thier cost, c, and revenue, r. c=500+200p and r= -p^2+800. what range can they price the cell phones so there will be a profit

a. less than $130 or more than $770

b. less than $200 or more than $500

c. between $130 and $770

d. between $200 and $500