There is a swimming pool in the Pearl Gymnasium. There are two inlet pipes A and B above the swimming pool, and a drain pipe below. Only open the A pipe for 3 hours, it can be filled with water in 3 hours, open the B pipe for 6 hours, and open the drain pipe for 4 hours to drain all the water in a pool. Now open the three pipes at the same time, how long will it take to fill the swimming pool?
明珠体育馆内有一个游泳池，游泳池上方有甲、乙两个进水管，下方有一个排水管．单开甲管3小时可注满水，单开乙管6小时可注满水，单开排水管4小时可将一池水全部排完．现在把三个管同时打开，多长时间能将游泳池注满？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/6) - (1/4)</gadget>
<output>-1/12 = around -0.083333</output>

<gadget id="calculator">(1/3) + (-1/12)</gadget>
<output>1/4 = around 0.25</output>

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

<result>4</result>