The train from Beijing to Guangzhou is 350 meters long and travels 22 meters per second. The train from Guangzhou to Beijing is 280 meters long and travels 20 meters per second. How many seconds.
从北京开往广州的列车长350米，每秒钟行驶22米，从广州开往北京的列车长280米，每秒钟行驶20米，两车在途中相遇，从车头相遇到车尾离开需要多少秒钟．
<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>