The perimeter of a rectangular photo frame is 90 cm. the length is twice the width. what are the length and width of the frame? (hint: the formula for perimeter is where w is the width, l is the length, and p is the perimeter.)

The formula for perimeter of a rectangle is
2(w + l) = P
Since the length of the frame is twice its width,
2(w + 2w) = 90cm. Thus, 2(3w) = 90cm
6w = 90cm
Therefore, w = 90/6.
w = 15

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.