Correct Answer: Rs. 3500

Solution : Use the formula below.
Simple interest = $\frac{\text{Principle×Rate×Time}}{100}$
Let's denote the principal amount (the sum borrowed) as P
Simple interest for the first 3 years at 3 percent per annum
= $\frac{3}{100}$ × P × 3
Simple interest for the next 5 years at 4 percent per annum
= $\frac{4}{100}$ × P × 5
Simple interest for the next 7 years at 6 percent per annum
= $\frac{6}{100}$ × P × 7
Total Interest = $\frac{3}{100}$ × P × 3 + $\frac{4}{100}$ × P × 5 + $\frac{6}{100}$ × P × 7
⇒ 2485 = $\frac{9P}{100}$ + $\frac{20P}{100}$ + $\frac{42P}{100}$ = $\frac{71P}{100}$
⇒ 248500 = 71P
⇒ P = $\frac{248500}{71}$ = 3500
Hence, the correct answer is Rs. 3500.