Explanation:

- Pipes A, B, and C have different filling/emptying rates.

- Pipe A: Fills the tank in 16 hours, so it fills 1/16 of the tank per hour.

- Pipe B: Fills the tank in 24 hours, so it fills 1/24 of the tank per hour.

- Pipe C: Empties the tank in 40 hours, so it removes 1/40 of the tank per hour.

- When all pipes work together:

$$

\text{Net rate} = \frac{1}{16} + \frac{1}{24} - \frac{1}{40}

$$

$$

= \frac{15}{240} + \frac{10}{240} - \frac{6}{240}

$$

$$

= \frac{19}{240} \text{ of the tank per hour}

$$

- In the first 8 hours, all pipes work together:

$$

\text{Part filled} = 8 \times \frac{19}{240} = \frac{152}{240} = \frac{19}{30}

$$

- After 8 hours, pipes B and C remain open:

$$

\text{New rate} = \frac{1}{24} - \frac{1}{40} = \frac{5}{120} - \frac{3}{120} = \frac{1}{60} \text{ of the tank per hour}

$$

- Remaining part of the tank:

$$

1 - \frac{19}{30} = \frac{11}{30}

$$

- Time to fill the remaining part:

$$

\frac{11}{30} \text{ divided by } \frac{1}{60} = 22 \text{ hours}

$$

- ? Correct Answer: 22 hours

-