Surekha borrowed a sum of money and returned it in two equal instalments of Rs. 5,547 each. If the rate of interest was $$7\frac{1}{2}\% $$  p.a. compounded yearly, then the total interest paid by her was:

$$7\frac{1}{2}\% \to \frac{3}{{10}}$$
\[\begin{array}{*{20}{c}} {}&{{\text{Principal}}}&{}&{{\text{Amout}}} \\ {{\text{One year}} \to }&{40 \times 43}&:&{43 \times 43} \\ {{\text{Two year}} \to }&{{{40}^2}}&:&{{{43}^2}} \end{array}\]
43 × 43 units → 5547
1 unit → 3
Interest in first year = 43 × 3 = 129 units
Second year = 1849 - 1600 = 249 units
Total interest = 129 + 249 = 378 units
378 units → 378 × 3 = Rs. 1134