I need help with the following questions.

How long does it take to read a disk with 10,000 cylinders, each containing four tracks of 2048 sectors? First, all the sectors of track 0 are to be read starting at sector 0, then all the sectors of track 1 starting at sector 0, and so on. The rotation time is 10 msec, and a seek takes 1 msec between adjacent cylinders and 20 msec for the worst case.

Switching between tracks of a cylinder can be done instantaneously.

The answer is 49,999 rotations but I don't know how to get the answer

I know that my profesor said reading that Reading the first 9999 cylinders thus takes 49,995

rotations and then you add 4. However I don't know why Reading the first 9999 cylinders thus takes 49,995 rotations

PLease help

Thanks