Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

Represent the unknown: Let $l$ = length Since the width is 30 feet less than the length, then $l-30$ = width RECALL: The perimeter $P$ of a rectangle is given by the formula $P=2l+2w$ where $l$=length and $w$ = width. Use the formula above to obtain: $P=2l+2w \\140=2l + 2(l-30) \\140=2l+2l-60 \\140=4l-60 \\140+60=4l-60+60 \\200=4l \\\frac{200}{4}=\frac{4l}{4} \\50=l$ The length is 50 feet. This means that the width is $50-30=20$ feet.