How do I write a system of equations for this?

 Kirma bought 12 feet of framing material to make a rectangular frame for her oil painting. She uses all the framing material and the length is twice the width.

?2021-04-07T20:55:09Z

Perimeter of rectangle, P = 2L + 2W = 12'
We know that L = 2W, so
                                     P = 2(2W) + 2W = 12'  ...........ANS
                                           6W = 12'
                                           W = 2'
                                           L = 2W = 2(2) = 4'
------------------
CHECK THE SOLUTION:
P = 2L + 2W = 2(4') + 2(2')
                     = 8' + 4'
                     = 12' .............CORRECT

fcas802021-04-07T19:44:53Z

12 = 2L + 2W
L = 2W