please help with precalculus

Question

A vehicle purchased for $ depreciates at a constant rate of  each year. Its value after t years can be modeled by the equation , where P is the original value of the vehicle.Determine the number of years that it takes for the vehicle to depreciate to $

Answer 1

Right, if we take 18% off, we are left with 82%, right?

12,000 = 22,400(0.82)^t

12,000/22,400 = 0.82^t

log(15/28) = tlog(0.82)

t = log(15/28)/log(0.82)

t = 3.145 years