If the area of a rectangle is 18 square inches and the length of the rectangle is twice it?

The question is not quite clear in what's it's asking. Presumably it's asking what is the length and width of the rectangle?

Let the length be 2x and the width be x:

2x*x = 18

2x2 = 18

Divide both sides by 2:

x2 = 9

Square root both sides:

x = 3

Therefore: length = 6 inches and width = 3 inches

If it is asking what the width is, and the length is twice the area, then the width would be .5 inches.

(L= A*2, L=36)

(36*.5=18)

(L*W=A)