Two cars, A and B, start at the same time from places A and B, which are 120 kilometers apart, and drive back and forth between places A and B. Car A travels 40 kilometers per hour, and car B travels 60 kilometers per hour. How many hours later, car B caught up with car A from behind for the second time.
甲、乙两车分别从相距120千米的A、B两地同时出发，在A、B两地之间不断往返行驶，甲车每小时行驶40千米，乙车每小时行驶60千米，多少小时后，乙车第二次从后面追上甲车．
<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">120 * (3/20)</gadget>
<output>18</output>

<result>18</result>