A project of ₹ 40,00,000 yielded annual profit of ₹ 6,00,000 after depreciation @ 12.50% but before tax…

Profit after depreciation and before tax is ₹ 6,00,000; deducting 50% tax leaves profit after tax of ₹ 3,00,000. Adding back annual non-cash depreciation of $12.5\% \times ₹\,40{,}00{,}000 = ₹\,5{,}00{,}000$ gives annual cash inflow of $₹\,3{,}00{,}000 + ₹\,5{,}00{,}000 = ₹\,8{,}00{,}000$, so $\text{Payback Period} = \frac{₹\,40{,}00{,}000}{₹\,8{,}00{,}000} = 5\text{ years}$.