The reliability of their new line of plastic extrusion machines, which have reported multiple problems recently, has piqued the curiosity of a plastics production facility. The machines typically run for 12 hours each day. Five machines were evaluated by engineers after running nonstop for 48 hours. One machine malfunctioned after 30 hours and another after 37 hours throughout the test.

At the end of the 48 hours, all other machines were still operational. Find the following out.

- The percentage failure rate, FR(%).

- The hourly failure rate FR(N).

- Mean time between failures.

- Calculate the number of working days the plant could endure before a machine broke down.