An investment project has the following discounted cash flows ($'000):
Year Discount rate
0% 10% 20%
0 90 90 90
1 30 27.3 25.0
2 30 24.8 29.8
3 30 22.5 17.4
4 30 20.5 14.5
30 5.1 (12.3)
The required rate of return on investment is 10% per annum. What is the discounted payback period of the investment project