An express train is 151 meters long and travels 15 meters per second, and a slow train is 254 meters long and travels 12 meters per second. How many seconds does it take for two cars to meet and leave.
一列快车全长151米，每秒钟行15米，一列慢车全长254米，每秒行12米．两车相向而行，从相遇到离开要多少秒钟．
<gadget id="calculator">151 + 254</gadget>
<output>405</output>

<gadget id="calculator">12 + 15</gadget>
<output>27</output>

<gadget id="calculator">405 / 27</gadget>
<output>15</output>

<result>15</result>