piece of wood is 4 meters long, and 20 decimeters are cut off, how many decimeters are left?
一根木头长4米，截掉了20分米，还剩几分米？
<gadget id="calculator">4 * 10</gadget>
<output>40</output>

<gadget id="calculator">40 - 20</gadget>
<output>20</output>

<result>20</result>