The value, V of a Tiffany lamp, worth $225 in 1965, increases at 15% per year. Its value in dollars t years after 1965 is given by $\displaystyle V = 225(1.15)^t$. Find the average value of the lamp over the period 1965-2000

-Can some1 please explain to me how to do this? I understand average value is 1 / b-a. But how do i set up the integral? from 0 to 45? or from 1965 - 2000 ?