We calculate displacement (change in position over a finite time interval) by integrating the velocity function.
We should note that we are given an initial position, s(0) = .8 . So, we calculate the position when t = 1.6 by adding the displacement on the time interval 0 ≤ t ≤ 1.6 to the starting position of .8:
s(1.6) = .8 + ∫01.6 sin(πt)dt