Let w=width
L= length
3w+1=l
Perimeter -2(l+w)
2(W+3w+1)=42
Divide both sides by 2
W+3w+1=21
Subtract 1
W+3w=20
Add like terms
4w=20
Divide both sides by 4
W=5
The width is 5 inches
3w+1=l
Input the width into the equation
3(5)+1=l
15+1=l
16=l
The length of the rectangle is 16 inches
The rectangle is 5 x 16 inches
