Rate is the ratio of a property or amount per unit time. The property can be distance or length, area, volume, mass, or any other property that can be associated with or that changes with time. In this case, the property is length. So, the rate is calculated by dividng the length by the time.
1713.5 ft / 57.5 s = 29.8 ft/s
The unit rate is 29.8 ft/s
