There are two water inlet pipes A and B in the reservoir. It needs to be filled at 18 hours when pipe A is opened alone, and pipe B needs to be filled at 24 hours when pipe B is opened alone. How long?
蓄水池有甲、乙两个进水管，单开甲管需18时注满，单开乙管需24时注满，如果要求12时注江满水池，那么甲、乙两管至少要合开多长时间？
<result>8</result>