Answer:
To find the estimated life of the machine in years, we need to first calculate the total depreciation of the machine.
Total depreciation = Cost of machine - Estimated trade-in value
Total depreciation = 855 - 129
Total depreciation = 726
Next, we can use the monthly straight-line depreciation to find the number of months it takes for the machine to depreciate by 726.
Monthly depreciation = 7
Number of months to depreciate = Total depreciation / Monthly depreciation
Number of months to depreciate = 726 / 7
Number of months to depreciate = 103.71
Finally, we can convert the number of months to years by dividing by 12.
Estimated life of machine = Number of months to depreciate / 12
Estimated life of machine = 103.71 / 12
Estimated life of machine = 8.64 years (rounded to two decimal places)
Therefore, the estimated life of the machine is approximately 8.64 years.