Suppose the demand for receiving work center $"Y"$ is $3$ parts per minute and the standard kanban container hold $15$ parts. Further assume that it takes one$-$and$-$a$-$half hours; that is$,1\mathrm{.}5$ hours, of lead time for a container to make a complete circuit from work center $"x"$ to work center $"Y"$ and back to $"x"$ again, including all setup, run, move, and wait time.

How many kanban containers are needed for the kanban system to work effectively and efficiently?