Uncle Wang wanted to build a 30-kilometer road, and he built 4 kilometers a day for 6 days. How many kilometers are left unrepaired?
王叔叔要修一条30千米长的公路，每天修4千米，修了6天．还有几千米没有修？
<gadget id="calculator">4 * 6</gadget>
<output>24</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<result>6</result>