To find the value decrease per month, we divide the total value decrease by the number of months.
Value decrease per month = Total value decrease / Number of months
In this case, the total value decrease is $4,000 and the number of months is 12.
Value decrease per month = $4,000 / 12
Value decrease per month = $333.33
Therefore, the value of the car decreases by $333.33 per month.
The correct answer is d) $333.33.