(15*20-180)/30=how much
(15*20-180)/30=多少
<gadget id="calculator">15 * 20</gadget>
<output>300</output>

<gadget id="calculator">300 - 180</gadget>
<output>120</output>

<gadget id="calculator">120 / 30</gadget>
<output>4</output>

<result>4</result>