Question 503617
I always recommend drawing a picture for word problems like this.
What can we say the width equals at this point? It is X
What can we say about the length at this points? It is 2x
-------------------------------------------------
Perimeter=the sum of all the sides.

So at this point the information we have is 2x+2x+x+x 
(since all we know about the side is x(we don't know this value) and that the length is two times as long (2x)
-------------------------------------------------
Set up the equation with all the information we currently have
2x+2x+x+x=360            (combine like terms)
6x=360                   (divide 6 on both sides to get x alone)
x=60
--------------------------------------------------
With this information, we now know the length and width.
Width=60
Since we had our length as 2x. Multiply 60 by 2

Width=60
Length=120
---------------------------------------------------
If you want to check add it all up!
60+60+120+120=360