John C. answered 04/21/20
BS in Mathematics/Computer Science with 34 years applied experience
The average of a function over an interval is computed as (1/width of interval) times the definite integral of the function evaluated over the interval. The indefinite integral of e^2x is (1/2)e^2x. So the answer is found by evaluating:
(1/2)*[(1/2)[e^8 - e^4]], or (1/4)[e^8 - e^4]
which equals about 731.6.