Let x be the width so the length will be 2x-4 . The perimeter can be found by the equation x+x+(2x-4)+(2x-4)=58. Notice I repeated the length and the width twice because you know there are two lengths and two widths in a rectangle, so continue solving by combining like terms 6x-8=58 the add 8 to both sides 6x=66 then divide both sides by 6 to obtain x=11, that's the width but they are asking you for the length so we said the length could be found by the equation 2x-4, now plug in the 11, 2(11)-4 and solve 22-4 equals 18cm which is the length.
