The equations we get are l = 6 + 2w (We get this from "The length of the rectangle is 6 more than 2 times the width.") and 2l + 2w = 140 (We get this from the perimeter. Two times the length plus two times the width equals the perimeter of a quadrilateral.)
The first equation can be written as l - 2w = 6
So now we have 2l + 2w = 140 l - 2w = 6 ____________ Add the two equations. We get 3l = 146