Final answer:
David's unit rate of speed is 45 miles per hour, as he drove 135 miles in 3 hours.
Step-by-step explanation:
The student has asked to find the unit rate of speed for David's travel. He drove 135 miles in 3 hours. To find the unit rate, we divide the total distance by the total time taken. Therefore, the calculation to find David's average speed, which is the unit rate, would be:
Unit rate = Total distance / Total time = 135 miles / 3 hours = 45 miles per hour (mph).
So, David's unit rate of speed is 45 mph. This means on average, David drove at a speed of 45 miles in one hour.