find average turnaround time using preemptive SJF ProcessArrival TimeBurst TimeP108P214P329P435 Select one:a. 13b. 20c. 10d. 14

To find the average turnaround time using preemptive Shortest Job First (SJF) scheduling, we need to follow these steps:

1. Sort the processes according to their arrival time. If the arrival time is the same, then sort according to the burst time. The process with the shortest burst time will be executed first.

2. Calculate the completion time for each process. The completion time is the time at which a process completes its execution.

3. Calculate the turnaround time for each process. The turnaround time is the difference between the completion time and the arrival time.

4. Calculate the average turnaround time. This is done by adding up all the turnaround times and dividing by the number of processes.

Let's calculate:

1. The processes are already sorted according to their arrival time and burst time.

2. The completion time for each process is as follows:

   • P1: 8 (as it arrives at 0 and has a burst time of 8)
   • P2: 14 (as it arrives at 1 and has a burst time of 4, but it has to wait for P1 to complete, so 8+4=12, but since P3 arrives at 2 and has a burst time of 9 which is less than the remaining time of P2, P2 will be preempted and will have to wait for P3 to complete. So, 12+9=21. Now, P2 can complete its execution. So, 21+2=23)
   • P3: 21 (as it arrives at 2 and has a burst time of 9, but it has to wait for P1 to complete, so 8+9=17)
   • P4: 35 (as it arrives at 3 and has a burst time of 5, but it has to wait for P1, P3, and P2 to complete, so 23+5=28)

3. The turnaround time for each process is as follows:

   • P1: 8-0 = 8
   • P2: 23-1 = 22
   • P3: 21-2 = 19
   • P4: 35-3 = 32

4. The average turnaround time is (8+22+19+32)/4 = 20.25

So, the closest answer is 20 (option b).