The accumulated value of the sinking fund is calculated using the formula:
\[ A = P \cdot \frac{(1 + r)^n - 1}{r}. \]
Here:
- \( P = 12,000 \),
- \( r = 0.05 \),
- \( n = 10 \),
- \( (1.05)^{10} \approx 1.6 \).
Substitute into the formula:
\[ A = 12,000 \cdot \frac{1.6 - 1}{0.05} = 12,000 \cdot \frac{0.6}{0.05} = 12,000 \cdot 12 = 1,44,000. \]
The surplus is:
\[ \text{Surplus} = A - 72,000 = 1,44,000 - 72,000 = Rs.72,000. \]