You have that the perimeter of a rectangle is 28. In order to find the values of length and width of the rectangle, you take into account the following formula for the perimeter of a rectangle:

where w is the width and l is the length. You have that the length l is twice the width w of the rectangle, that is l=2w. By replacing this expression for l into theformula for the calculation of the perimeter you obtain:

Thus, you have that P = 6w. You solve this equation for w, and also replace the value of P, just as follow:

Then, the width is 4.66. The length is:

length = 9.33