Two people, A and B, run in the same direction from the same point on a circular runway with a circumference of 400 meters. A runs 7 meters per second, and B runs 5 meters per second. Then they arrive at the starting point at the same time from the start to the first time. How many seconds did it take?
甲、乙两人在周长为400米的环形跑道上，从同一地点同时同向跑步，甲每秒跑7米，乙每秒跑5米，那么两人从出发到第一次同时到达出发点用了多少秒？
<gadget id="calculator">7 / 7</gadget>
<output>1</output>

<gadget id="calculator">400 * 1</gadget>
<output>400</output>

<result>400</result>