Suppose that the following processes arrive for execution at the times indicated. Each process will run for the amount of time listed. In answering the question, use nonpreemptive scheduling, and base all decisions on the information you have at the time the decision must be made. If two or more processes are identical in terms of scheduling criterion, you should give precedence to the process that has the smallest process ID (PID) number.

 PID ArrivalTime BurstTime 0 0 21 1 0 12 2 0 32 

What is the average waiting time for these processes with the Shortest Job First (SJF) scheduling algorithm?