Answer:
3.5 years, or 3 and a half years.
Explanation:
Depreciation = (Initial investment - salvage value) / number of useful life = ($280,000 - $30,000) / 5 = $250,000 / 5 = $50,000
Net cash inflow = Annual net income + depreciation = $20,000 + $50,000 = $80,000
Payback period = Initial investment / Net cash flow = $280,000 / $80,000 = 3.5 years, or 3 and a half years.