To find Ashley's rate of speed in miles per hour, you will use the formula
Rate = Distance/Time.
First, you should fill in what you know. In this case, you know the distance is 2.5 miles, and the time is 0.75 hours. Now, you simply plug in the known variables to the formula to get Rate = 2.5 miles / 0.75 hours. After dividing, you reach the answer Rate = 3.333333 (or 3 and 1/3) miles/hour.