A boy cycles 3km due east in 12min and then 4km due west in 18min.
a. (i) Calculate his average speed for the entire trip.
b. (ii) Calculate his average velocity for the entire trip, taking the starting point as the origin and east as the positive direction.
c. (iii) Explain why the magnitudes obtained in parts (i) and (ii) are different even though the journey lasted 30min.