It took 7 days to build a canal, 50 meters a day, and the remaining tasks continued at the original speed, and the task could be completed in 6 days. How long is this canal in meters?
修一条水渠，修了7天，每天修50米，剩下的任务按原来的速度继续修，6天可以完成任务．这条水渠全长多少米？
<gadget id="calculator">7 + 6</gadget>
<output>13</output>

<gadget id="calculator">50 * 13</gadget>
<output>650</output>

<result>650</result>