Answer: 21 degrees
Step-by-step explanation:
In the evening, the temperature is 28 degrees and by midnight it has dropped 31 degrees lower, the temperature by midnight will be:
= 28° - 31°
= -3°
Between midnight and 4 am it goes down 6 more degrees. The temperature by 4am will be:
= -3° - 6°
= -9°
Then, by 9 am, the temperature goes up 30 degrees, the temperature at 9 am will then be:
= -9° + 30°
= 21°
