Explanation:

- First, add A and B's capital: Rs54,000 + Rs36,000 = Rs90,000 (total current capital).

- A and B together will now share 2/3rd. So, total capital for the firm (if C’s 1/3rd is included) should be: Let total capital = X.

- C's share = 1/3, so C's capital = 1/3 × X.

- A+B's share = 2/3 × X = Rs90,000, so X = Rs90,000 × (3/2) = Rs1,35,000.

- C's capital = 1/3 × Rs1,35,000 = Rs45,000.

- Option 1 (Rs90,000) is wrong because it's A+B’s current total.

- Option 3 (Rs5,400) is too low and irrelevant.

- Option 4 (Rs36,000) is B’s capital, not C’s required amount.

- Correct answer: Option 2, Rs45,000.