First, you need to determine how quickly the carriage is moving per unit time. In this case, we can figure this out from the distance it traveled over the amount of time it took.
If the carriage traveled 30 miles in 6 hours, 30÷6=5. The carriage is traveling 5 miles per hour.
We can now use this speed to find how far the carriage will travel over 8 hours. 5x8=40 miles.
Let me know if you have any questions!