Answer: 18.8%
Explanation:
Simple rate of return on investment = Incremental net operating income / investment
Incremental net income = Operating savings - Annual cost
= 145,000 - 420,000/6 years
= $75,000
Net investment = Cost of new machine - salvage value of old
= 420,000 - 21,000
= $399,000
Return on investment = 75,000/399,000
= 18.8%