A truckload of materials was purchased for $36,000. They were sorted Out into the following grades whose market rate is shown as under: No, of Units Grade X 5,000 Grade Y 3,000 Grade Z 2,000 Selling rate per unit $ 4.80 $ 4.00 $ 2.00 Find out the purchase rate per unit of each grade of the material assuming all grades yield the same rate of profit