Cylinder access request Sequence : 4,34,10,7,19,73,2,15,6,20
Shortest Seek Time First : The tracks which are closer to current disk head position should be serviced first.
Current Cylinder Position = 50
So, 50 --> 34 --> 20 --> 19 --> 15 --> 10 --> 7 --> 6 --> 4 --> 2 --> 73 will be disc access Sequence.
Time = [(50 - 34) + (34 - 20) + (20 - 19) + (19 - 15) + (15 - 10) + (10 - 7) + (7 - 6) + (6 - 4) + (4 - 2) + (73 - 2)] x 1
= 16 + 14 + 1 +4 + 5 + 3 + 1 + 2 + 2 +71
= 119ms
So,option (4) is correct option.