Explanation:

To solve the problem, let's first define the situation clearly and calculate step-by-step:

- A's work rate: A can finish the work in 18 days, i.e., A does \(\frac{1}{18}\) of the work per day.

- B's work rate: B can finish the work in 24 days, i.e., B does \(\frac{1}{24}\) of the work per day.

- Combined rate of A and B:

$$

\frac{1}{18} + \frac{1}{24} = \frac{4 + 3}{72} = \frac{7}{72} \ \text{of work per day}

$$

- Together, A and B can complete \(\frac{7}{72}\) of the work per day.

- Work to finish in 8 days:

To finish the work in 8 days, they together (A, B, and C) must do \(\frac{1}{8}\) of the work per day.

- C's work rate:

Let C's work rate be \(x\), then:

$$

\frac{7}{72} + x = \frac{1}{8}

$$

Solving for \(x\):

$$

x = \frac{1}{8} - \frac{7}{72} = \frac{9 - 7}{72} = \frac{2}{72} = \frac{1}{36}

$$

- C's salary calculation:

C does \(\frac{1}{36}\) of the work per day, so for 8 days, C does:

$$

\frac{8}{36} = \frac{2}{9} \ \text{of the total work}

$$

C's share of the salary:

$$

\frac{2}{9} \times 30960 = 6880 \ \text{Rs}

$$

- Final Decision:

- Option 4: Rs. 6880

- Correct answer highlighted and marked with a green tick:

Correct Answer: Option 4: Rs. 6880