Explanation:

- Pipe A can fill the entire tank in 12 hours, giving it an hourly rate of 1/12 of the tank.

- Pipe B fills it in 20 hours, contributing 1/20 of the tank per hour.

- Pipe C empties the tank in 15 hours, with a rate of -1/15 of the tank per hour.

- Initially, the combined rate per hour for 5 hours is \((1/12 + 1/20 - 1/15)\).

- After 5 hours:

- A's efficiency increases by 20%, so it now fills at 1.2/12 (or 1/10) of the tank per hour.

- B's efficiency doubles, so it fills at 2/20 (or 1/10) of the tank per hour.

- C’s efficiency decreases by 50%, so it empties at -1/30 of the tank per hour.

- The new combined rate per hour is \( (1/10 + 1/10 - 1/30) \).

- Calculate total tank filled in both phases and determine total time for more precision.

- Given all the math, the correct answer is:

Option:4- 9 hours

YOUR ANSWER IS WRONG