Answer:
130.77%
Step-by-step explanation:
depreciation expense per year using straight method = (purchase cost - salvage value) / useful life = ($86,000 - $7,000) / 10 = $7,900
total costs = depreciation expense + operating and energy costs = $7,900 + $4,190 = $12,090
average rate of return = total savings / total costs = $15,810 / $12,090 = 1.30769 = 130.77%