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 number of cylinders?

Select one:

a$.6000$ cylinders

b$.20$ cylinders

c$.400$ cylinders

d$.12000$ cylinders

e$.800$ cylinders