Did you make a sketch?
Jack has 3000 feet of fencing available to enclose a rectangular field.
One side of the field lies along a river, so only 3 sides require fencing.
(a) Express the area of the rectangle as a function of ,
where is the length of the side parallel to the river.
(b) Graph . .For what value of is the area largest?The area of the field is: . Code:~ + ~ ~ ~ ~ ~ ~ + ~ | | y| |y | | * - - - - - - * x
The total fencing is: .
Since Jack has 3000 feet of fencing: . 
Substitute  into : . (a)
If we graph , it looks like this:The maximum occurs when .Code:| | * | * : * | * : * | * : * |* : * | : --*-----------+-----------*-- | 1500 3000