A system consists of two identical units, Unit 1 and Unit 2. Normally Unit 1 is up. If Unit 1 fails, Unit 2 goes up with perfect switching and repair starts on Unit 1 immediately. If Unit 2 fails while Unit 1 is under repair, repair does not start on Unit 1 until repair on Unit 1 is completed. The MTTF for each unit is 1000 hours and MTTR is 10 hours. Find: a) the MTBF for the system and, b) compare it to MTTF for the system when there is no repair.