To answer this question, we need to use the concept of unit rate. In this case, we need to find the rate in miles per hour (per one hour). To get this rate, we can proceed as follows:
Therefore, the rate in miles per hour is 4 miles per hour. We only need to divide the total miles (12miles) by 3 hours, and the result was 4 miles/hour (a unit rate, miles per one hour.)