$6\mathrm{.}15$ Susan is considering buying a $2011$ Smart ForTwo costing $$21,635$ and finds that

the retaining values of the vehicle over next five years are as follows:

Iii Percent of the total value retained after $36$ months: $28\%$

Ill Percent of the total value retained after $60$ months: $17\%$

If her interest rate is $6\%$ compounded annually, what is the ownership cost of

the vehicle over three years? five years?