Explanation:

- The problem involves compound interest with two different amounts over different time periods.

- In 3 years, the sum grows to Rs 7,800.

- In 5 years, the same sum becomes Rs 11,232.

- Let's find the rate using the compound interest formula:

A = P(1 + r/100)^n, where A is the amount, P is the principal, r is the rate, and n is the number of years.

- The ratio of amounts over the two periods gives:

11,232/7,800 = (1 + r/100)^2.

Simplifying:

(1 + r/100)^2 = 1.44

- Solving for (1 + r/100), we get:

1 + r/100 = 1.2

- This implies r = 20%.

- Option 2: 20 is correct.

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