Final answer:
The student's average speed walking to school was calculated to be 5 km/hr by dividing the total distance of 7.5 km by the total time of 1.5 hours.
Step-by-step explanation:
To calculate the student's average speed for walking to school, we can use the formula:
Average Speed = Total Distance / Total Time
In this case, the student walked a distance of 7.5 km in 1.5 hours. To find the average speed, we divide the distance by the time:
Average Speed = 7.5 km / 1.5 hours = 5 km/hr
Therefore, the student's average speed was 5 km/hr, which corresponds to option (b).