W = width; L= length

2W+2L=14 : Formula for perimeter

W=L-3 : From problem description

2(L-3)+2L=14 : Substitute (l - 3) for width

L-3+L=7 :Divide all by 2

2L-3=7 : Simplify

2L=10 : Add 3 to both sides

L=5 : Divide both sides by 2

W=2 : Because width is 3 less than length

2(2) +2(5) = 14 : The proof

4 + 10 = 14

14=14

2W+2L=14 : Formula for perimeter

W=L-3 : From problem description

2(L-3)+2L=14 : Substitute (l - 3) for width

L-3+L=7 :Divide all by 2

2L-3=7 : Simplify

2L=10 : Add 3 to both sides

L=5 : Divide both sides by 2

W=2 : Because width is 3 less than length

2(2) +2(5) = 14 : The proof

4 + 10 = 14

14=14