150/4 = 37.5cm. You divide by four because there are four sides on a rectangle. But 37.5 is the cm of a square. Since it says one of the sides is 15cm greater, you subtract 37.5 - 15 = 27.5cm on 2 of the width. While the other 2 lengths are greater than the width by 15 cm, so you add 15 to 37.5 which gives you 52.5cm. So the 2 width are 27.5cm and the length is 52.5cm.