Train A is 370 meters long and travels 15 meters per second; train B is 350 meters long and travels 21 meters per second. The two trains are traveling in the same direction. How long does it take for train B to catch up with train A and completely overtake it?
甲火车长370米，每秒行15米；乙火车长350米，每秒行21米，两车同向行驶，乙车从追上甲车到完全超过甲车需要多长时间？
<gadget id="calculator">370 + 350</gadget>
<output>720</output>

<gadget id="calculator">21 - 15</gadget>
<output>6</output>

<gadget id="calculator">720 / 6</gadget>
<output>120</output>

<result>120</result>