Answer:
rate of return: 16.67%
Explanation:
unadjusted rate of return
[tex]\frac{average \: return}{average \: investment}[/tex]
Average investment
Assuming no salvage value:
(beginning investment + ending investing)/2
(4,800 + 0 )/ 2 = 2,400
cost savings: 720
depreciation: 4,800 / 15 = 320
average  return 400
400/2400 = 16.67%