Rate of change = (amount of change) / (time for the change)
Amount of change = (temp at the end) minus (temp at the beginning)
Amount of change = (70°F) minus (62°F) = 8°F
Time for the change = (time at the end) minus (time at the beginning)
Time for the change = (1200 - 0800) = 4 hours
Rate of change = (8°F) / (4 hours)
Rate of change = 2°F per hour