There are three circular runways, the centers of which are all at the flagpoles in the playground. A, B, and C are running in the same direction in the inner circle, the middle circle, and the outer circle respectively. At the beginning, all three were due east of the flagpole. The runway in the inner circle is (1/5) kilometers long, the middle circle is (1/4) kilometers long, and the outer circle is (3/8) kilometers long. A runs 3.5 kilometers per hour, B runs 4 kilometers per hour, and C runs 5 kilometers per hour, then they start at the same time, how many hours later, the three return to the starting point at the same time for the first time.
三条圆形跑道，圆心都在操场中的旗杆处．甲、乙、丙三个人分别在里圈、中圈、外圈，沿同样的方向跑步．开始时，三个人都在旗杆的正东方向．里圈跑道长(1/5)公里，中圈长(1/4)公里，外圈长(3/8)公里．甲每小时跑3.5公里，乙每小时跑4公里，丙每小时跑5公里，那么他们同时出发，多少小时以后，三人第一次同时回到出发点．
<gadget id="calculator">2 * 2 * 2 * 2 * 2 * 3 * 5 * 7</gadget>
<output>3_360</output>

<gadget id="calculator">3_360 / 560</gadget>
<output>6</output>

<result>6</result>