Xiaodong buys 8 kilograms of watermelon for 20 yuan and gets back 4 yuan. How much is it per kilogram of watermelon?
小冬用20元钱买8千克西瓜，找回4元，每千克西瓜多少元？
<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 8</gadget>
<output>2</output>

<result>2</result>