QUESTION 4: (25 Marks) a) A multiprogramming operating system that using binary semaphores for concurrency control is executing one (1) producer (process-D) and three (3) consumers (process- A, B, and C) concurrently, following Figure-3 depicting snapshots of the system state at various timestamps, explain what is happing in the system at timestamp-1 through timestamp-7. (15 Marks) III ITACD D TRAC THAO b) Find the number of page faults caused by optimal page replacement algorithms. number of page frames is 3. consider the context string R=1,2,3,4,1,2,5,1,2,3,4,5. (10 marks)