Answer:
The temperature change was -2 degrees per hour.
Explanation:
1st hour (8pm) it dropped down to 4 degrees.
2nd hour (9pm) it dropped down to 2 degrees.
3rd hour (10pm) it dropped down to 0 degrees.
4th hour (11pm) it dropped down to -2 degrees.
5th hour (12am/midnight) it dropped down to -4 degrees