Length = 7 + Width
Width = Width
Area = (Length)(Width)
Use Substitution: 120 in2 = (7 + Width)(Width)
Notice I replaced Area with "120 in2" and Length with "7+ Width" because Area is equal to 120 in2 in this problem and Length in terms of the Width is given as 7 more than the Width.
Lastly, Solve for the Width as follows:
120 in2 = (7 + Width)(Width) Let w = Width.
120 in2 = (7 + w)(w) Simplify the right-hand side of the equation.
120 in2 = w2+ 7w Subtract 120 in2 from both sides of the equation.
0 = w2+7w -120 in2 Factor the quadratic expression on the right-hand side of the equation.
0 = (w - 8) (w+15) Use the zero-factor property to solve for w or the width.
w = 8 or -15
Width cannot be negative. Therefore, width has to be 8 inches and length 7 more than that or 15 inches.