The manager of Vintage Time Video Machine Parlor is responsible for ensuring that all six of his machines are in good condition. Machines frequently need attention but can normally be returned to service quickly. On an average, each machine requires attention five times each hour. The manager averages 4 minutes per repair.

a. What percentage of each hour is the manager fixing machines?

b. On an average, how many machines are broken down and waiting for repair?

c. On an average, how many minutes in an hour are machines waiting for repair or being repaired?