The marginal profit (in dollars per unit) for producing a certain item is modeled by M(p)=−4p+20, where p is the selling price per unit in dollars. Which statement best describes how the total profit changes as the price increases from \3to7?
a) Profit decreases throughout this price range because M(p) is negative for all p between 3 and 7.
b) Profit increases until the price reaches 5 and decreases thereafter.
c) Profit decreases until the price reaches 5 and increases thereafter.
d) Profit increases throughout this price range because M(p) is positive for all p between 3 and 7.