the anwerÂ
the main formula concerning such a problem is as follow:
v= Delta x  / Delta t =Δx / Δt = xf  - xi / tf - ti
f = final value, i=initial value
Find the average velocity for each time period.
when t is in [1, 3]Â Â
soÂ
v=  xf  - xi / tf - ti = 10.6 -1 .6 =9 / 3 - 1 =9 / 2 = 4.5
your answer is correct
when t is in [2, 3]Â
v = 10.6 - 5.5 / 3 - 2 = 5.1 m/s Â
your answer is correct
when t is in [3, 5]Â
v = 24.9 - 10.6 / 5-3 = 7.15 m /s
your answer is correct
when t is in [3, 4]Â
 v = 17.1 - 10.6 / 4 -3 =  6.5 m/s
your answer is correct
the instantaneous velocity when t =3
v = Δx / Δt = 10.6 / 3 = 3.53 m/sÂ