a$.$ A disk drive spins at $7200$ RPM$,$ has a sector size of $512$ bytes, and holds $160$ sectors per track. Estimate the sustained transfer rate of this drive$-$in megabytes per second. Suppose that the drive has $7000$ cylinders, $20$ tracks per cylinder, a head switch time $($from one platter to another$)$ of $0\mathrm{.}5$ millisecond, and an adjacent cylinder seek time of $2$ milliseconds. What will be an accurate estimate of the sustained transfer rate for a transfer of $100$ cylinders of data?