Question 46916
Let the width of the rectangle be x feet. So, its length will be (3x-2)feet. Since area is 21 square feet. The equation is 
(3x-2).x=21
3x^2-2x-21=0
Solving either by factoring or using quadratic formula,x=3 or -7/3.
The length of the rectangle=(3x-2)=7 feet and width=3. 
Note:-7/3 is not valid for getting the solution.