b) Find the average velocity for the given time intervals ,

Question

t = 4 s. and t = 6 s.

t = 11 s. and t = 12 s.

Answer 1

as always, v = ∆s/∆t = (s(6)-s(4))/(6-4)
Since you neglected to indicate the values of s, or the equation connecting s with t, the rest is up to you.