The train from Shanghai to Hangzhou is 350 meters long and the speed is 22 meters per second. The train from Hangzhou to Shanghai is 280 meters long and the speed is 20 meters per second. How many seconds does it take for the tail to leave?
从上海开往杭州的列车长350米，行驶速度为22米/秒，从杭州开往上海的列车长280米，行驶速度为20米/秒，若两车在途中相遇，从车头相遇到车尾离开需要多少秒？
<gadget id="calculator">350 + 280</gadget>
<output>630</output>

<gadget id="calculator">22 + 20</gadget>
<output>42</output>

<gadget id="calculator">630 / 42</gadget>
<output>15</output>

<result>15</result>