The distance between A and B is 540 kilometers. A large truck starts from A to B and travels 40 kilometers per hour. At the same time, a car starts from B to A and travels 50 kilometers per hour. The two vehicles face each other. and go. After meeting each other on the way, the two cars headed opposite each other, and returned immediately after arriving at their destinations. How many hours will it take from departure to second encounter?
A、B两地相距540千米，大卡车从A地出发开往B地，每小时行40千米，同时小轿车从B地出发开往A地，每小时行50千米，两车相向而行．在途中相遇以后，两车又相背而行，各自到达目的地后立即返回．从出发到第二次相遇时需要多少小时？
<gadget id="calculator">40 + 50</gadget>
<output>90</output>

<gadget id="calculator">3 / 90</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">540 * (1/30)</gadget>
<output>18</output>

<result>18</result>