pre cal questions... soo confused

(Worried) Ok there are three questions from my precal homework that i CANNOT figure out. its driving me nuts. Any help?

Suppose that the manufacturer of a gas clothes dryer has found that, when the unit price is *p* dollars, the revenue *R* (in dollars) is given by the equation below. *R*(*p*) = -4*p*2 + 2480*p*

What unit price for the dryer should be established to maximize revenue?

$

What is the maximum revenue?

$

David has available 550 yards of fencing and wishes to enclose a rectangular area. (a) Express the area

*A* of the rectangle as a function of the width

*x* of the rectangle.

*A*(

*x*) =

http://www.webassign.net/v4images/sm_preview.gif
(b) For what value of

*x* is the area largest?

*x* =

(c) What is the maximum area?

square yards

A farmer with 4000 meters of fencing wants to enclose a rectangular plot that borders on a river. If the farmer does not fence the side along the river, what is the largest area that can be enclosed?

square meters