if a car is 61,400 and lose 20% each year. How many years will it take for the value to reach 5,000
5000 = 61400 (.80)^x
5000/61400 = .8^x
log (5000/61400) = x log(.8)
x = log(5000/61400)/log(.8) = 11.24 years
y=61,400*(1.00-.2)x put in years and guess and check