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 useful capacity of a track?

Select one:

a$.8$ KB

b$.$ none

c$.12\mathrm{.}5$ KB

d$.4\mathrm{.}096$ KB

e$.10240$ Bytes