A circular runway has a circumference of 400 meters. A and B are in the same direction, and C is facing away from them. They start from the same place at the same time. A runs 6 meters, B runs 4 meters, and C runs 5 meters every second. How many seconds will it take for the three to meet for the first time after departure?
一环形跑道周长400米，甲与乙同向，丙与他们背向，同时同地出发，每秒钟甲跑6米，乙跑4米，丙跑5米．出发后三人第一次相遇要多少秒？
<result>400</result>