The watermelon in the supermarket in Kyoto is 4.5 yuan per kilogram. My mother bought a watermelon of 3.8 kilograms and paid 20 yuan. How much should I get back?
京都超市的西瓜每千克4.5元，妈妈买了一个西瓜3.8千克，付出20元，应找回多少钱呢？
<gadget id="calculator">4.5 * 3.8</gadget>
<output>17.1</output>

<gadget id="calculator">20 - 17.1</gadget>
<output>2.9</output>

<result>2.9</result>