580.8
The average rate of change of a function f(x) between x-values x1 and x2 is given by
... average rate of change = (f(x2) -f(x1))/(x2 -x1)
For your function
... f(x) = 12·3^x
and x-values 0 and 5, this becomes ...
... average rate of change = (f(5) -f(0))/(5 -0) = (2916 -12)/5 = 580.8