Find the time that it takes Rick to walk the first half of the distance, that is, to travel a distance D/2 at speed v?

t = (D/2) / v

Explanation:

Speed is the distance traveled per unit of time.

Speed = Distance / Time

Represent:

speed as v,

distance as D,

time as t

v = D / t

by cross multiplication,

vt = D

divide both sides of the equation by v

t = D/v

But it is half of the distance, so,

t = (D/2) / v

t = D/2v