A truck drives a distance d$=26\mathrm{.}6$ m in the positive x direction in a time t$1=21\mathrm{.}2$ s$,$ at which point the truck brakes, coming to rest in t$2=9\mathrm{.}23$ s$.$

 A: What was the trucks average velocity in the horizontal direction, in meters per second, during the t$1$ time period? 

 B: Assuming the truck started from rest and moved with a constant acceleration, what was the acceleration, in meters per squared second, during time interval t$1?$ 

C: What was the trucks instantaneous velocity in the horizontal direction, in meters per second, when it began braking?

D: Using the result from Part $($c$),$ what was the trucks horizontal component of acceleration, in meters per squared second, during the braking period?