Two engineering teams repair 121 kilometers of roads. Team A repairs 3.8 kilometers every day, and team B repairs 4.7 kilometers every day. Team A works for 5 days first, and then the two teams work together, and it will take a few days to finish.
两个工程队修121千米的路，甲队每天修3.8千米，乙队每天修4.7千米．甲队先工作5天，后两队合修，还需要几天才能修完．
<gadget id="calculator">3.8 * 5</gadget>
<output>19</output>

<gadget id="calculator">121 - 19</gadget>
<output>102</output>

<gadget id="calculator">3.8 + 4.7</gadget>
<output>8.5</output>

<gadget id="calculator">102 / 8.5</gadget>
<output>12</output>

<result>12</result>