To find the unit rate of passengers per car, you divide the total number of passengers by the total number of cars.
\[ \text{Unit rate} = \frac{\text{Total passengers}}{\text{Total cars}} = \frac{764 \text{ passengers}}{191 \text{ cars}} \]
Now perform the division:
\[ \frac{764}{191} \approx 4 \]
So, the unit rate is approximately 4 passengers per car.