$\frac{0}{1}$ Points$]$

BERRAPCALCBR$72\mathrm{.}5\mathrm{.}033.$

After $t$ hours a freight train is $s(t)=17t^2-2t^3$ miles due north of its starting point $($for $0t9).$

$($a$)$ Find its velocity at time $t=3$ hours.

$m\frac{i}{h}r$

$($b$)$ Find its velocity at time $t=7$ hours.

$m\frac{i}{h}r$

$($c$)$ Find its acceleration at time $t=1$ hour.