Acampground owner has 24002400 m of fencing. he wants to enclose a rectangular field bordering a river, with no fencing along the river. (see the sketch.) let x represent the width of the field. (a) write an expression for the length of the field as a function of x.

We define variables:
 x = represent the width of the field
 y = represent the length of the field
 We write the perimeter (with no fencing along the river):
 2400 = 2x + y
 We clear y:
 y = 2400-2x
 
 an expression for the length of the field as a function of x is:
 y = 2400-2x

The correct answer is: b