Answer:
The length of the rectangle: 3x
The width of the rectangle: x
Theres 2 lengths and 2 widths for every rectangle.
So the full perimeter is 3x+x+3x+x = 8x
8x;
= perimeter
= 40 inches
8x=40
x=40/8
x=5 inches
Length is 3x, substitute in for x
l = 3(5)
l = 15