Answer:
C 7ft/yr
Step-by-step explanation:
The given points are not all on the same line, so the average will vary depending on the interval of interest.
Over the interval [1, 11] years, the average rate of change of height is ...
change in height / change in years = (80 -10)/(11 -1) = 70/10 = 7 . . . ft/yr
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On the interval [11, 15] years, the average rate of change is ...
(105 -80)/(15 -11) = 25/4 = 6.25 . . . ft/yr
Even on this interval, the closest answer choice is C.
