Two people, A and B, start at the same time from the opposite corners of a wall with a side length of 56 meters, and run around the wall in the same direction. A runs 7 meters per second, and B runs 5 meters per second. After how many seconds does A see B for the first time?
甲乙两人分别从一个边长56米围墙的对角顶点同时出发，绕围墙按同一方向跑，甲每秒跑7米，乙每秒跑5米，经过多少秒钟甲第一次看见乙？
<gadget id="calculator">7 - 5</gadget>
<output>2</output>

<gadget id="calculator">56 / 2</gadget>
<output>28</output>

<result>28</result>