$1.$ Define CPU scheduling and explain its importance in the context of operating system functionality. Discuss how CPU scheduling policies impact system performance.

$2.$ Consider a system with three processes P$1,$ P$2,$ and P$3,$ with CPU burst times of $10,5,$ and $8$ milliseconds respectively. Using the First$-$Come, First$-$Served $($FCFS$)$ scheduling algorithm, calculate the average waiting time for these processes if they arrive in the order P$1,$ P$2,$ P$3.$