Rectangular Photograph Word Problem

A rectangular photograph is twice as long as it is wide. The perimeter of the photograph is 84 cm.
Find the length and the width of the photograph.

x = width
2x = length {twice as long as it is wide} 

Perimeter of a rectangle is 2(width) + 2(length) 

2x + 2(2x) = 84 {perimeter is 2(width) + 2(length)}
2x + 4x = 84 {multiplied}
6x = 84 {combined like terms}
x = 14 {divided each side by 6}
2x = 28 {substituted 14, in for x, into 2x} 

width = 14 cm
length = 28 cm

- Algebra House