A can run around a circular track in 40 seconds. Now A and B run from the same point in opposite directions at the same time and meet A after 15 seconds. How many seconds does it take for B to run a circle?
甲用40秒可绕一环行跑道跑一圈，现在甲、乙两人从同一点同时向相反方向跑，15秒后与甲相遇，那么乙跑一圈所用的时间是多少秒．
<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>