Question

The length of a rectangle is 3cm greater than its width. The perimeter is 24 cm. What are the dimensions of the rectangle.

Answer 1

OK, so if it was square, the sides would be 6cm each for a perimeter of 24cm.
Therefore, if the length is 3cm greater than the its width, add the 3cm to each of one side, you've got a rectangle that measures 9 x 3 x 9 x 3 which makes 24.

Answer 2

Or, do it like that ^ which is a much better way. Nicely put @Mokeira .