A home is to be built on a rectangular plot of land with a perimeter of 800 feet. If the length is 2

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A home is to be built on a rectangular plot of land with a perimeter of 800 feet. If the length is 20 feet less than 3 times the width, what are the dimensions of the rectangular plot?

Set up equations:
(1) 2l + 2w = 800
(2) l = 3w - 20

Substitute (2) into (1)
2(3w - 20) + 2w = 800
6w - 40 + 2w = 800

Group the w terms
8w - 40 = 800

Add 40 to each side
8w = 840

Divide each side by 8
w = 105

Substitute w = 105 into (2)
l = 3(105) - 20
l = 315 - 20
l = 295