Explanation:

- A receives 1/15th of the total profit. Therefore, A's share is \( \frac{1}{15} \times \text{Total Profit} \).

- The remaining profit, which is \( \frac{14}{15} \times \text{Total Profit} \), is shared between B and C in the ratio 3:4.

- Let's denote the total profit as \( X \).

- A's share = \( X/15 \).

- Remaining profit = \( 14X/15 \).

- B's share = \( \frac{3}{7} \times \frac{14X}{15} = \frac{42X}{105} = \frac{2X}{5} \).

- C's share = \( \frac{4}{7} \times \frac{14X}{15} = \frac{56X}{105} = \frac{8X}{15} \).

- Given that the difference between C's and A's share is Rs. 2800:

- \( \frac{8X}{15} - \frac{X}{15} = 2800 \).

- \( \frac{7X}{15} = 2800 \).

- \( X = 6000 \) (Total profit).

Now:

- B's share = \( \frac{2X}{5} = \frac{2 \times 6000}{5} = 2400 \).

- Correct Answer:

- Rs. 2400 (Option 4)