We're asked to calculate the average velocity of a particle given a change in position and a change in time.
Recall that the average velocity of an object, , is related to the change in position (displacement,) over change in time Δt:
Velocity is a vector, which means the signs really matter (unlike speed, which is a scalar.)
(a) For the particle in this problem, we're first asked to calculate its average velocity between t1 and t2. We're given that x1 = 3.4 cm, x2 = 8.0 cm, t1 = −5.4 s, and t2 = 5.6 s.