Given the following data, calculate the payback period for the proposed investment in a digital mammography scanner by Rockpile Radiology:
Equipment cost: $300,000
Cash Inflow year 1: $50,000
Cash Inflow year 2: $75,000
Cash Inflow year 3: $100,000
Cash Inflow year 4: $125,000
Cash Inflow year 5: $150,000
Corporate cost of capital: 6.5%
Disposal value: $30,000