Answer
length = 50 feet
width = 20 feet
Work Step by Step
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.
