Question: how to calculate sjf preemptive?
Answer: Step 1) At time= 1, Process P3 arrives. ... 
Step 2) At time =2, process P1 arrives and is added to the waiting queue. ... 
Step 3) At time = 3, process P4 will finish its execution. ... 
Step 4) At time = 4, process P5 arrives and is added to the waiting queue.