Consider the following three process designs to organize a call center with $12$ employees. The center handles calls for two customer types. Type $1$ customers call with credit card related questions and type $2$ customers call with questions related to the online account opening. On a busy day the call center receives $60$ calls per hour from type $1$ customers and $30$ calls per hour from type $2$ customers. It takes on average $2$ minutes to service both kinds of calls.

Process design $1$: $6$ employees handle type $1$ calls; the other $6$ employees handle type $2$ calls