$A$ tap can fill a tank in $6$ $h$. After half the tank is filled,three more similar taps are opened. What is the total time taken to fill the tank completely?

$A$ tank can be filled by pipe $A$ in $2$ $h$ and pipe $B$ in $6$ $h$. At $10$ $am$ pipe $A$ was opened. At what time will the tank be filled if pipe $B$ is opened at $11$ $am$?

An oil drum can be filled with oil in $40$ $min$ by a filling pipe. Another outlet pipe can empty the entire drum in $60$ $min$. The outlet pipe was opened when $\frac{2}{3}$ part of the drum was filled with oil and closed after $15$ $min$. What time will it take to fill the drum when the filling pipe is opened now?

$18$ pumps can fill a reservoir of capacity $1440 \text{ kilo liter}$ in $5 \text{ hours}$. How many $\text{hours}$ are required to fill a reservoir of capacity $1920 \text{ kilo liter}$ by $8$ pumps?

There are two taps $A$ and $B$ to fill up a water tank. The tank can be filled in $40$ $min,$ if both taps are on. The same tank can be filled in $60$ $min,$ if tap $A$ alone is on. How much time (in $minutes$) will tap $B$ alone take to fill up the same tank?

Two taps $A$ and $B$ can fill a tank in $10$ $hours$ and $12$ $hours$ respectively. If both taps are opened at $10 \text{ am}$,at what time (in $\text{pm}$) should tap $A$ be closed so that the tank is completely filled at exactly $4 \text{ pm}$?