Depreciation on a car can be determined by the formula V = C(1 – r)', where V is the value of the car after t years, C is the original cost,
and r is the rate of depreciation.
If a car's cost, when new, is $15,000, the rate of depreciation is 30%,
and the value of the car now is $3,000, how old is the car to the
nearest tenth of a year?