The formula for the perimeter of a rectangle p=21+2w

The formula for the perimeter of a rectangle is 2l+2w. which means twice the length and twice the width added to together.

if you mean this:

x=21+2x

minus x on both sides

0=21-x

add 21 on both sides

21=-x

x=-21

than you subsitute

2*-21=-42

-42+21 = - 21

The perimeter is than - 21