A basketball is 80 yuan, Xiaoqiang has 500 yuan, bought 6 basketballs, how much money is left.
一个篮球80元，小强有500元，买了6个篮球，还剩多少元．
<gadget id="calculator">80 * 6</gadget>
<output>480</output>

<gadget id="calculator">500 - 480</gadget>
<output>20</output>

<result>20</result>