Pipes P and Q can fill a completely empty tank in 24 minutes and in 36 minutes, respectively, when opened independently. Pipe R can empty the completely filled tank in 30 minutes. Initially all the three pipes P, Q and R are opened simultaneously. After how many minutes should pipe Q be closed so that the tank is filled in exactly 1 hour?

Three taps A, B, and C can fill an empty tank in 30 minutes, 20 minutes, and 10 minutes respectively. When the tank is empty, all three taps are opened. Taps A, B, and C release chemical solutions P, Q, and R respectively. What is the proportion of solution R in the tank after 3 minutes?

Two inlet pipes J and T can fill a tank in 120 minutes and 144 minutes respectively. If an outlet pipe Z is opened along with them, all three pipes together fill the tank in 240 minutes. How long will pipe Z alone take to empty the full tank?