Question 14
Each valve $A,$ $B,$ and $C,$ when open, releases water into a tank at its own constant rate. With all three valves open, the tank fills in $1$ hour, with only valves $A$ and $C$ open it takes $1.5$ hours, and with only valves $B$ and $C$ open it takes $2$ hours. The number of hours required with only valves $A$ and $B$ open is