A train is 210 meters long and travels 18 meters per second; B train is 140 meters long and travels 13 meters per second. Train B is in front and train A is behind, and the two trains are traveling on a double track. How many seconds does it take for train A to overtake train B from behind?
甲火车长210米，每秒行18米；乙火车长140米，每秒行13米．乙火车在前，甲火车在后，两火车在双轨车道上行驶．甲火车从后面追上到完全超过乙火车要用多少秒？
<gadget id="calculator">210 + 140</gadget>
<output>350</output>

<gadget id="calculator">18 - 13</gadget>
<output>5</output>

<gadget id="calculator">350 / 5</gadget>
<output>70</output>

<result>70</result>