A rope is 24.2 meters long, 7.8 meters are used for the first time, and 3.5 meters are used for the second time, how many meters are left?
一条绳子长24.2米，第一次用去7.8米，第二次用去3.5米，还剩多少米？
<gadget id="calculator">24.2 - 7.8 - 3.5</gadget>
<output>12.9</output>

<result>12.9</result>