From Mechanics

Using the result from part a) for the acceleration,

\displaystyle \begin{align} & v=\int{a}dt \\ & \\ & =\int{\left( \frac{2t}{5} \right)}dt \\ & \\ & =\frac{{{t}^{2}}}{5}+c \\ & \\ & t=0,\ v=8\ \Rightarrow \ c=8 \\ & \\ & v=\frac{{{t}^{2}}}{5}+8 \end{align}