A and B run around a playground with a circumference of 400 meters, and A runs 6 meters per second. B runs 4 meters per second. If they start from the starting point in the same direction at the same time. According to this speed. After how many seconds can A catch up with B?
甲、乙绕一个周长为400米的操场跑步，甲每秒跑6米．乙每秒跑4米．如果他们同时同向从起点出发．照这样的速度．多少秒后甲能追上乙？
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">400 / 2</gadget>
<output>200</output>

<result>200</result>