Question 175327
Let l = the length of the rectangle

Let w = the width of the rectangle

2*l+2*w=42  (Equation #1)

l = 2*w-3  (Equation #2)

Substitute equation 1 for "l" in Equation #2

2*(2w-3)+2w=42

4*w-6+2*w=42

Collect like terms

6w=48
Solve for w
w=8

Substitute w=8 into Equation #1

2*l+2*8=42

2*l+16=42
Solve for l

2*l=26

So l=13.