Answer
$a_{A}=1.9\space m/s^{2}$
$a_{B}=0\space m/s^{2}$
$a_{C}=3.3\space m/s^{2}$
Work Step by Step
The slope of that segment is the average acceleration for each segment.
$a_{A}=\frac{40\space m/s-0\space m/s}{21\space s-0\space s}=1.9\space m/s^{2}$
$a_{B}=\frac{40\space m/s-40\space m/s}{48\space s-21\space s}=0\space m/s^{2}$
$a_{C}=\frac{80\space m/s-40\space m/s}{60\space s-48\space s}=3.3\space m/s^{2}$
