Two teams, A and B, are digging a canal. Team A digs 20 meters a day, and team B digs 40 meters a day. The dug will be completed in 15 days. How long is the canal?
甲乙两队同挖一条渠，甲队每天挖20米，乙队每天挖40米，15天正好挖完，这条水渠有多长？
<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">60 * 15</gadget>
<output>900</output>

<result>900</result>