Two trains leave opposite directions at the same time from two stations A and B. Train A travels 120 kilometers per hour, and train B travels 90 kilometers per hour. The two trains meet at a distance of 30 kilometers from the midpoint. Find the time when the two cars meet.
两列火车同时从甲乙两站相向开出，甲车每小时行120千米，乙车每小时行90千米，两车在离中点30千米处相遇．求两车相遇的时间．
<gadget id="calculator">120 - 90</gadget>
<output>30</output>

<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">30 * (1/15)</gadget>
<output>2</output>

<result>2</result>