A rope is 9 decimeters long, and 20 centimeters are used up, how long is left?
一根绳子长9分米，用去20厘米，还剩多长？
<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">9 - 2</gadget>
<output>7</output>

<result>7</result>