A takes 40 minutes to walk a certain distance, and B takes 30 minutes to walk a certain distance. Starting from the same place, A walks for 5 minutes first, and then B starts to catch up. How long does it take for B to catch up with A?
甲走一段路用40分钟，乙走一段路用30分钟．从同一地点出发，甲先走5分钟，乙再开始追，乙多少分钟才能追上甲．
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) - (1/40)</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">5 / (1/120)</gadget>
<output>600</output>

<gadget id="calculator">(1/40) * 600</gadget>
<output>15</output>

<result>15</result>