how do i solve this word problem (based on real numbers)

cant figure out the operations to use

In January 2008, the temperature in parts of Minnesota fell from 48ºF to -12ºF over a 24 hour period. what was the average temperature change per hour

A. (1 1/2)

B.-(1 1/2)

C. -2.5ºF

D. 2.5ºF