A pool has a water inlet pipe and a water outlet pipe. Open the water inlet pipe alone for 10 minutes to fill the empty pool, and open the water outlet pipe for 15 minutes to empty the whole pool. Now open the water inlet pipe to fill the empty pool with water, and then open it again after 4 minutes Out of the water pipe, wait a few more minutes to fill the pool?
一个水池有一进水管和一出水管，单开进水管10分钟可将空水池注满，单开出水管15分钟可将整池水放空，现先打开进水管给空水池注水，4分钟后又打开出水管，再等几分钟可以注满水池？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 4</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) - (1/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(3/5) / (1/30)</gadget>
<output>18</output>

<result>18</result>