The distance between two piers is 4.2 kilometers. Pier B is in front, and Pier A is behind. A passenger ship departs from Pier B, traveling an average of 500 meters per minute. At the same time, a speedboat set off from Wharf A and caught up with the passenger ship after sailing for 12 minutes. How many meters does the speedboat travel on average per minute?
两个码头之间的路程是4.2千米，乙码头在前，甲码头在后，一艘客轮从乙码头出发，平均每分钟行500米．同时一艘快艇从甲码头出发，航行了12分钟就追上了客轮，快艇平均每分钟行多少米？
<gadget id="calculator">4.2 * 1_000</gadget>
<output>4_200</output>

<gadget id="calculator">500 * 12</gadget>
<output>6_000</output>

<gadget id="calculator">4_200 + 6_000</gadget>
<output>10_200</output>

<gadget id="calculator">10_200 / 12</gadget>
<output>850</output>

<result>850</result>