3.1 A system adopts a priority-based preemptive scheduling where the initial priority of a process increases by 1 after every 5 ms. In a recorded time span, the system has four processes, P1, P2, P3 and P4, as shown in the following table.

Process ID	Initial Priority	Arrival Time in ms	Total CPU time in ms
P1	1	0	15
P2	3	5	7.5
P3	2	10	5
P4	2	15	10

Draw a timing diagram similar to Figure 3.7 and find the turnaround time for each process. Assume that the dispatcher takes 2.5 milliseconds for a process switch.