$[15$ points$]$ Considering the following three processes, with their arriving time, priority, and the length of their CPU bursts $($in milliseconds$)$:

$\backslash$table$[[$Process$,$CPU$-$Burst Time,Arrive Time,Priority$],[1,20,0,2],[2,15,11,3],[3,6,12,1($highest priority$)]]$

a$)$ Draw four Gantt charts to illustrate the execution of these processes using the following scheduling algorithms: FCFS$,$ RR $($quantum $=10),$ non$-$preemptive SJF$,$ and preemptive priority scheduling.

b$)$ Calculate the average waiting time of the three processes under each of the four scheduling algorithms.$[15$ points$]$ Considering the following three processes, with their arriving time, priority, and the length of their CPU bursts $($in milliseconds$)$:

$\backslash$table$[[$Process$,$CPU$-$Burst Time,Arrive Time,Priority$],[1,20,0,2],[2,15,11,3],[3,6,12,1($highest priority$)]]$

a$)$ Draw four Gantt charts to illustrate the execution of these processes using the following scheduling algorithms: FCFS$,$ RR $($quantum $=10),$ non$-$preemptive SJF$,$ and preemptive priority scheduling.

b$)$ Calculate the average waiting time of the three processes under each of the four scheduling algorithms.