Hard Drive Seek Time using FIFO, SSF, SCAN
@greybeard why he divided by 2
on average we will need to wait for half a rotation of the disk for the correct sector to come under the head. Thus, on average, the rotational latency is half the time it takes the disk to make a complete revolution.

do I need to multiply this by the number of tracks moved?
No. Because average rotational time is the time to move head from one sector to any other sector in same track. This movement is done by disk rotation.

In your question we will consider any sector in given track. So when track changes from 30 to 27, it takes 3 track movement and 1 average rotation so time 3*0.1+5

In general, total time = seek time + rotating latency

Seek time : time to change track

Edited

(3+102+19+76+39+106+31+54+56)*0.1 + number_of_time_movement_occured * rotational_latency
= 486 * 0.1 + 9 * 5
= 48.6 + 45
= 93.6