Toyota Repair: car price

Question
I need help in determing the price of a car.

I bought a Toyotall Corolla for $18,000 in 2013.
monthly payment is $400/month.
I pay off 18 months already. That would add up to $7200. I am giving the car to my parent, They will continue to pay off the payments that are left. But of the 18 months that I pay for the car and used it,

1. How much do I hope that my parent owe me for the 18 months payment? I am thinking $7200

2. If the car is payoff in 4 years.  How much will the car be worth to sell at (max) price or what the Toyotall Corolla would be worth?

Answer
The rule of thumb for Toyotas is that after 5 years they are worth about 50% of what is was sold for. Usually you do not get paid for what you have already paid due to depreciation,  so $7200 is unreasonable, at this time the value of the car is approximately $14000, so the difference would be $4000, this is depreciation, so if they offer you #4000 plus take over payments that would be more than fair.