A tank is partially filled with water up to a volume of L liters. At the same instant, 30 holes are created at the bottom of the tank, and an inlet pipe is connected to the tank. If the tank takes 12 hours to empty with 30 holes open, and if only 15 holes are open, the tank takes 24 hours to empty. If (3M + 6) holes are created, then the tank is emptied in 6 hours. Find the value of M.
1
6
2
9
3
12
4
15
5
18