It takes 1.5 minutes to travel between machines, 2 minutes to load a machine, 1 minute to unload a machine and 0.5 minutes to inspect and pack a finished part. Machine runs automatically for 15 minutes. Operators cost $20 per hour and machines cost $45 per hour.

a-) What is the maximum number of machines that can be assigned to an operator without creating machine idle time during a repeating cycle?

b-) What assignment minimizes the cost per unit produced?