Exponential Decay
The value of the car can be modeled with an exponential decay function:

Where V(t) is the resale or residual value of the car after t years, Vo is the initial value (purchased price), and r is the decay rate.
The car was purchased for Vo = $26,000 and the price decays by r = 35% = 0.35 per year, thus our function is:

The resale value after t = 4 years is:

The resale value is $4,641