Final answer:
Ricardo's average rate of speed is 56 miles per hour.
Step-by-step explanation:
The average rate of speed is calculated by dividing the total distance traveled by the total time taken. In this case, Ricardo drives 28 miles in half an hour, so his average rate of speed is:
Average speed = Distance / Time = 28 miles / 0.5 hour = 56 miles per hour
Therefore, Ricardo's average rate of speed is 56 miles per hour.