Write the unit rate for the situation. 210mi in 3hr

I think you could say the unit rate would be 210 miles/3 hours = 70 miles/hr.

To determine the unit rate, all you would have to do is simply, take the measurement of distance and divide by the unit of time, so it would be 210 miles/3 hours = 70 miles/hr.

Unit simply means one. So find the rate the object is moving in 1 (unit of time) in this case hour.