Answer:
The answer to your question is a) 21:00  b) -14°C
Step-by-step explanation:
Data
Temperature at noon = 10°C
rate = 2°C/hour
a) Do a chart to solve this problem
      Time      Temperature
      12:00         10°C
       13:00         8°C
       14:00         6°C
       15:00         4°C
       16:00         2°C
       17:00          0°C
       18:00         -2°C
       19:00         -4°C
       20:00        -6°C
       21:00         -8°C
b)
      22:00         -10°C
       23:00        -12°C
      24:00         -14°C