A chair is 24 yuan, buy 15 chairs, pay 500 yuan, how much is left.
一把椅子24元，买15把椅子，付了500元，还剩多少元．
<gadget id="calculator">24 * 15</gadget>
<output>360</output>

<gadget id="calculator">500 - 360</gadget>
<output>140</output>

<result>140</result>