Lisa traveled to her cabin on the lake and back. The trip there took five hours and the trip back took six hours. She averaged 45 km/h on the return trip. Whats the average speed of the trip there?
Anytime you know two of the three variables you can calculate the third! So you are trying to find the average speed for the trip there, and you know the time but not the distance. Presumably the distance is the same in both directions, so we can calculate that from the return trip.
Since the distance = rate * time, we know the rate was 45 km/h and the time was 6 hours, so the distance is 45km/h * 6h = 270 kilometers. For the trip back, we know that rate = distance / time = (270 km/h ) / 5 hours = 54 kilometers per hour.
Don't let it throw you when the problem does not seem to have enough information; you can calculate the information you need from what has been given.