Its annualized ROI is 0.83 or 83%.
Since, $75,000 is the profit for 6 years, we must divide it by 6 to get the annual profit.
75000 / 6 = 12500 annual profit.
Return on Investment is equal to Net Profit divided by Total Asset.
In this case, the total asset is the initial investment of $15000.
ROI = 12500 / 15000 = 0.83
0.83 x 100% = 83 %.