roll of rope is 10 meters long, 4.2 meters are used for skipping rope, and 1.8 meters are used for bundling. How many meters of this roll of rope are left?
一卷绳子长10米，做跳绳用去了4.2米，捆包裹用了1.8米，这卷绳子还剩多少米？
<gadget id="calculator">4.2 + 1.8</gadget>
<output>6</output>

<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<result>4</result>