Two people A and B are running along a 400-meter circular track. If they run with their backs on the same ground at the same time, after they meet, A's speed will increase by 4 meters per second, and B's speed will decrease by 4 meters per second. As a result, both of them take 10 seconds. At the same time, return to the original place, what is the original speed of A?
甲、乙两人沿400米环形跑道跑步，如果同时同地背向跑，两人相遇后，甲的速度每秒增加4米，乙的速度每秒减少4米，结果两人都用10秒同时回到原地，原来甲的速度是多少？
<gadget id="calculator">400 / 10</gadget>
<output>40</output>

<gadget id="calculator">40 - 4</gadget>
<output>36</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">36 / 2</gadget>
<output>18</output>

<result>18</result>