It has been 30 days to build a tunnel with a length of 3,600 meters, and there are still 1,200 meters left to be repaired. How many meters are repaired per day on average?
修一条长3600米的隧道，已经修了30天，还剩1200米没修，平均每天修多少米．
<gadget id="calculator">3_600 - 1_200</gadget>
<output>2_400</output>

<gadget id="calculator">2_400 / 30</gadget>
<output>80</output>

<result>80</result>