Final answer:
Zach will have walked 20 kilometers in total after 5 trips to school.
Step-by-step explanation:
Since the relationship is directly proportional, we can find the constant of proportionality by dividing the total distance walked by the number of trips. In this case, the constant is 12 km divided by 3 trips, which is 4 km. So, Zach walks 4 km for each trip to school.
Therefore, after 5 trips to school, Zach will have walked a total of 5 trips times 4 km per trip, which is 20 km in total.
Learn more about Calculating distance in a directly proportional relationship