A canal is 531 meters long. It has been repaired for 6 days, and there are 21 meters left to be repaired. How many meters are repaired per day on average?
一条水渠全长531米．已经修了6天，还剩21米没修，平均每天修多少米？
<gadget id="calculator">531 - 21</gadget>
<output>510</output>

<gadget id="calculator">510 / 6</gadget>
<output>85</output>

<result>85</result>