A can run around a 600-meter runway in 40 seconds. B runs in the opposite direction and meets A every 15 seconds. How many seconds does it take for B to run a lap?
甲用40秒可绕600米的跑道跑一圈，乙反方向跑，每隔15秒与甲相遇一次，乙跑一圈要多少秒？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/15) - (1/40)</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">1 / (1/24)</gadget>
<output>24</output>

<result>24</result>