Answer
Unit for slope: "riders/day per $\$ 1$ increase of the price of a ride "
For every rise by $\$ 1$ of the price of the ride, the number of rides per day decreases by $4500$.
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 "riders per day", and
p in "price (in dollars) per ride"
So, the slope here is measured in
"riders/day per $\$ 1$ increase of the price a ride "
Our demand function from part (a), $q=-4500p+41,500$
has slope $-4500$, which we interpret:
For every rise by $\$ 1$ of the price of the ride, the number of rides per day decreases by 4500.
