Answer:
The answer to your question is "The temperature drops 3.125°F each minute".
Explanation:
Data
Initial temperature = 63°F      Initial time = 11:30 am
Final temperature = -12°F      Final time = 11:54 am
Process
1.- Calculate the difference of minutes
  11:54 - 11:30 = 24 min
2.- Calculate the difference of temperature
  63°F - (-12°F) = 63°F + 12°F = 75°F
3.- Divide the difference of temperature by the difference of time
        75/24 = 3.125
4.- Conclusion
  The temperature drops 3.125°F each minute.