Given l = length and w = width, The perimeter of a rectangle is 2l + 2w, we have:

- l = 3w
- 2l + 2w = 56

2(3w) + 2w = 56

6w + 2w = 56

To solve this equation for w, we type it in our math engine and we get:

w =

**7**

To solve for l, we substitute w = 7 into equation (1):

l = 3(7)

l =

**21**