A hard disk of $20$ sectors per track and $400$ tracks per surface in $15$ double$-$sided platters disk, and platters rotates at a speed of $2400$ RPM with average seek time $30$ ms$.$ Each sector contains a block of size $512$ bytes and gap size between blocks $128$ bytes. What is the total capacity of the disk?Select one:a$.76$ MBb$.117\mathrm{.}18$MBc$.146\mathrm{.}5$ MBd$.$ nonee. $61$ MB