The table below represents the atmospheric temperature at a location as a function of the altitude:

Altitude
(in thousand feet)
x
Temperature
(in °C)
f (x)
15
4
20
−6
25
−16
30
−26


The average rate of change of the function between x = 15 to x = 25 is ___degrees Celsius per thousand feet and represents the rate of change of temperature per thousand feet