Answer
Unit for slope:
"rides/day per one zonar increase of the price a ride "
For every rise by one zonar of the price of the ride, the number of rides per day decreases by 2 million.
Work Step by Step
In the demand function $q=mx+b,$
the slope m is measured in (units of q) per (one unit of p)
Here, q is measured in "million rides per day", and
p in "price (in zonars) per ride"
So, the slope here is measured in
"riders/day per one zonar increase of the price a ride "
Our demand function from part (a), $q=-2p+24$
has slope $-2$, which we interpret:
For every rise by one zonar of the price of the ride, the number of rides per day decreases by 2 million.
