Disk requests come in to the disk driver for cylinders $25,40,7,32,22,5$ and $15,$ in

that order.

A s eek takes $20$ msec per cylinder moved. How much s eek time is needed for

$($a$)$ First$-$come, first served.

$($b$)$ Shortest Seek First $($SSF$).$

$($c$)$ Elevator algorithm $($initially moving upward$).$

In all cases, the arm is initially at cylinder $17$