Answer: C.76.8
Explanation:
We know that the average rate of change of any function f(x) from x=a to x= b is given by :-

Given : Finbar invested money in a transportation stock whose growth is modeled by the function
, where x represents number of days.
Then , the average rate of change of any function f(x) from day 11 to day 15 is given by :-

Hence, the approximate average rate of change from day 11 to day 15 = 76.8
Thus , the correct answer is option C. 76.8