Xiao Ming takes 20 yuan to buy melons, and the melons are 7.5 yuan per kilogram. Xiaoming bought 2.6 kilograms. How much should he get back?
小明拿20元去买甜瓜，甜瓜每千克7.5元，小明买了2.6千克，应找回多少钱呢？
<gadget id="calculator">7.5 * 2.6</gadget>
<output>19.5</output>

<gadget id="calculator">20 - 19.5</gadget>
<output>0.5</output>

<result>0.5</result>