Aunt Li bought 5 kilograms of apples, and the price of the apples is 3.2 yuan per kilogram. After Aunt Wang paid 20 yuan, how much should she get back?
李阿姨买了5千克苹果，苹果的售价是3.2元/千克，王阿姨付出20元后，应该找回多少元．
<gadget id="calculator">3.2 * 5</gadget>
<output>16</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<result>4</result>