The operating time of a system is 24 hours per day, Monday through Saturday. Failure of the system occurs as follows.
Monday: No failure
Tuesday: 5 A. M. to 7 A. M.
Wednesday: No failure
Thursday: 4 P.M. to 8 P.M.
Friday: 8 A. M. to 11 A. M.
Saturday: No failure
What is the MTBF of the system?