**Answer:**

3 x 2 = 6 years to get Rs. 1324

**Step-by-step explanation:**

This is a mathematical relationship that transcends currencies. In other words, it also applies to Dollars, Pounds and Yen.

“Annual compound interest” is a phrase of dubious meaning. The process is a “compound interest problem”, but the item I think you are looking for is simply the amount of interest.

Month 0: interest: 0 balance: 4,000

Month 6: interest; 200 balance: 4,200

Month 12: interest 210 balance: 4,410 12-month total interest: 410

Month 18: interest: 220.5 balance: 4,630.5 12-month total interest: 430.5

Month 24: interest: 231.525 balance: 4,862.025 12-month total interest: 452.025

Month 30: int: 243.10125 bal: 5,105.12625 12-month total int: 474.35125

Keep expanding this progression until the 12-month total interest meets or exceeds 1324, the answer will be the number of months in the last line.