Isaac works in the school cafeteria. He is packing boxed lunches into crates for students to take on a field trip. The crates are shaped like cubes and have a volume of one cubic foot each. The crates are packed in a van that is shaped like a rectangular prism. The van has a volume of 150 cubic feet. The floor of the van is completely covered by a layer of 30 crates. The height of the van that is filled is ___ feet.