Instantaneous and Average Velocity

Consider the following statements regarding the position function $s(t) = t^2 + 2t + 1$.

I. The instantaneous velocity is given by the derivative, $s'(t) = 2t + 2$.
II. At time $t=3$, the instantaneous velocity is $s'(3) = 2(3) + 2 = 8$.
III. The average velocity on the interval $[3, 4]$ is equal to the instantaneous velocity at $t=3.5$.

Which of the statements above is/are true?