Question 14604
Okay, picture the rectangle. The length of one side is x, i.e. a value we don't yet know so we use a letter to indicate that value. The other side is twice that length. So, the other side is 2x. When you add up the sides (x + 2x + x + 2x) you get a value of 480. Putting this into an algebraic expression (instead of words) gives {{{6x = 480}}}. This can be solved easily.
6x = 480
x = 80 [dividing both sides by 6]
That is the length of one side.
2x = 160 [multiplying both sides by 2]
That is the length of the other side.