Write a word problem involving fractions about the distance between two friend house that are in opposite directions from the library?

Person A's house is 8km from the library, and his friend B's house is in the opposite direction. Suppose it takes person A 3h to walk to B's house and back, and 1h to walk to the library and back, how far is B's house to the library (assuming person A always walks with constant speed) ?

Answer: 16km (involves fractions because you use ratio of time and ratio of distances)