Final answer:
Assuming equal time for both halves of the trip because of the constant speed condition, the average speed of the car for the entire 150-mile journey is 5 miles per hour (mph), calculated by dividing the distance by the total time of 30 hours.
Step-by-step explanation:
The student is asking about the average speed of a car for its entire journey. If a car travels 150 miles in total and it takes 15 hours to cover the first 75 miles, one would need to know the time taken to cover the second half of the trip to calculate the total time and thus the average speed. However, since that information is not provided, we assume that the time is the same for the second half due to the 'constant speed' condition. Therefore, the car would also take 15 hours to cover the remaining 75 miles, making the total time 30 hours for 150 miles. The average speed Vavg is calculated by dividing the total distance by the total time, which yields:
Vavg = total distance / total time = 150 miles / 30 hours = 5 miles per hour (mph).
This is the car's average speed for the entire journey.