The length of a rectangle is three times it's width. If the perimeter of the rectangle is 64, find its length and width

set up an equation for the perimeter

l = length w = width

2l + 2w = 64

set up another equation as you know the length is 3 times the width

w = 3l

subsitute w = 3l into the 2l + 2w = 64

2l + 2 (3l) = 64

solve for l

2l + 6l = 64

8l = 64

length = 8

subsitute into w = 3l

w = 3 (8)

width = 24