Mom bought 2.5 kilograms of tomatoes at the vegetable market. After paying the salesperson 20 yuan, she got back 5 yuan. How much is it per kilogram of tomatoes?
妈妈在菜市场买了2.5千克西红柿，付给售货员20元钱后，找回5元，每千克西红柿多少钱？
<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">15 / 2.5</gadget>
<output>6</output>

<result>6</result>