The number of years n for a piece of machinery to depreciate to a known salvage value can be found using the formula

n =(log s log i) / log(1 d)

where s is the salvage value of the machinery, i is its initial value, and d is the annual rate of depreciation. (a) How many years will it take for a piece of machinery to decline in value from $90,000 to $10,000 if the annual rate of depreciation is 0.20 (20%)?.

b) How many years will it take for a piece of machinery to lose half of its value if the annual rate of depreciation is 15%?