Answer:
If the value of Mike's car decreased by 30%, we can calculate the new value of the car as follows:
New value = Original value - (Percentage decrease × Original value)
Percentage decrease = 30%
Original value = 12000
New value = 12000 - (0.30 × 12000)
New value = 12000 - 3600
New value = 8400
Therefore, at the end of the decrease, the value of Mike's car was 8400.