analyze this from another gpt: let me explain clearly and precisely why the "9 years" answer is incorrect. Why Using "Net Income" Alone (9 Years) Is Wrong: The payback period cannot be calculated using net income alone. Net Income includes depreciation expense, which is a non-cash expense. Depreciation is subtracted from revenues to get net income, but it does not involve actual cash payments. Since depreciation is deducted from net income, the actual cash inflow (money available to pay back the investment) is higher than net income