The distance (in kilometres) travelled by a car t hours after it starts is given by s(t)=3t2+2t, where 0≤t≤5.
a. (a) Calculate s(1) and s(4).
b. (b) Determine the average velocity of the car during the time interval t∈[1,4].
c. (c) State the units of your answer in part (b) and interpret its sign in the context of the journey.