A water pipe of type A can fill the pool in 30 minutes, and a water pipe of type B can fill the pool in 40 minutes. Now use 3 Type A water pipes for 5 minutes, then open several Type B water pipes, and the pool will be filled in 2 minutes and 30 seconds. How many Type B water pipes were opened?
一根甲种水管30分钟可以灌满水池，一根乙种水管40分钟可以灌满水池．现先用3根甲种水管放5分钟，再打开若干根乙种水管，2分30秒就灌满水池．打开了多少根乙种水管？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 16</gadget>
<output>1/16 = around 0.0625</output>

<gadget id="calculator">(1/4) / (1/16)</gadget>
<output>4</output>

<result>4</result>