Arbitrarily define the instantaneous vector height of a person as the displacement vector from the point halfway

Question:

Arbitrarily define the “instantaneous vector height” of a person as the displacement vector from the point halfway between his or her feet to the top of the head. Make an order-of-magnitude estimate of the total vector height of all the people in a city of population 100 000 (a) at 10 o’clock on a Tuesday morning, and (b) at 5 o’clock on a Saturday morning. Explain your reasoning.