Question 450624
l = length   w = width

Start with what you know and form equations.  The perimeter is the distance of all sides added..length + length + width + width is equal to the perimeter or 2(length) + 2 (width) = perimeter

So: you could say 2l + 2w = 56 then you know that the length is 8 less then twice the width.  l = 2w - 8..now that we have 2 equations we can find the solutions.

Since we know that l = 2w - 8 we can substite l from this equation into the other one.

2(2w - 8) + 2w = 56  
4w - 16 + 2w = 56
6w - 16 = 56   add 16 to both sides
6w = 72  divide both sides by 6
w = 12
Now we know that w = 12...so plug that back into an equation
2l + 2(12) = 56
2l + 24 = 56  subtract 24 from both sides
2l = 32  divide both sides by 2
l = 16

Make sure these numbers fit both equations..so now you know the 
Width of the rectangle is 12 cm and the length is 16 cm.