SOLUTION: how do i find the width of a rectangle when the perimeter is 280 feet and the length is 20 feet less than 3 times the width?

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Question 799258: how do i find the width of a rectangle when the perimeter is 280 feet and the length is 20 feet less than 3 times the width?
Answer by Finavon(81) About Me  (Show Source):
You can put this solution on YOUR website!
Let sides be l and b
perimeter = 2*(l+b)
l=3b-20
substituting for l
perimeter= 2*(3b-20+b) = 6b-40+2b = 8b-40
280=8b-40 so 320=8b
b=40
l=120-20=100
rectangle is 40cm by 100cm
Check: perimeter=40+40+100+100=280