In the given case, Bill has already incurred $4,000 on the restoration and now he has two options for the car.
In the first option he can sell the car for $6200 after sending additional Cost of $2400. So net loss under this option shall be = (4000+2400)-6200 = $200
In the second option, he can sell the car for $3800 without incurring any additional cost. So net loss under this option shall be = 4000-3800 = $200
We can see that the net loss is same under both the options so Bill can go for any option.