Mom bought 5 kilograms of rice and 1.5 kilograms of lean meat from the supermarket, and the total cost was 31.5 yuan. It is known that rice is 1.8 yuan per kilogram. How much is lean meat per kilogram?
妈妈从超市买回来5千克大米和1.5千克瘦肉，一共用去了31.5元，已知大米每千克1.8元，请问瘦肉每千克多少元？
<gadget id="calculator">1.8 * 5</gadget>
<output>9</output>

<gadget id="calculator">31.5 - 9</gadget>
<output>22.5</output>

<gadget id="calculator">22.5 / 1.5</gadget>
<output>15</output>

<result>15</result>