fox and a rabbit have a jumping competition. The fox jumps 4.5 meters each time, and the rabbit jumps 2.4 meters each time. They both jump once per second. During the race, a trap is set every 15 meters from the starting point. At what second, the fox and the rabbit fall into the trap at the same time for the first time.
狐狸和兔子进行跳跃比赛，狐狸每次跳4.5米，兔子每次跳2.4米，它们都是每秒跳一次．比赛途中，从起点开始每隔15米设一个陷阱，第多少秒钟时狐狸和兔子第一次同时掉进陷阱．
<gadget id="calculator">4.5 - 2.4</gadget>
<output>2.1</output>

<gadget id="calculator">15 / 2.1</gadget>
<output>7.142857</output>

<result>7.142857</result>