Three Flood gates A, B and C can fill a reservoir in 6 hours. After working all together for 2 hours, flood gate C is closed. Flood gates A and B can fill the remaining part in 7 hours. The number of hours taken by flood gate A alone to fill the reservoir is:
If โโโ means โรโ, โรทโ means โ+โ, โ+โ means โโโ and โรโ means โรทโ, then what is the value of 23 โ 4 รท 15 ร 3 + 10 ?