How is a cars speed an example of unit rate?

A car's speed is a unit rate because it expresses the rate of change of distance with respect to time, specifically, the distance traveled *per unit of time*.

For example, 60 miles per hour means the car travels 60 miles (distance) in 1 hour (time). The "per hour" signifies the "unit" of time – it's the rate for *one* hour. Other examples would be meters per second, kilometers per hour, etc. All these are unit rates because they specify the amount of something (distance) per single unit of another (time).