Q82

The head of a hard disk serves requests following the shortest seek time first $\textsf{(SSTF)}$ policy. The head is initially positioned at track number $180$. Which of the request sets will cause the head to change its direction after servicing every request assuming that the head does not change direction if there is a tie in $\textsf{SSTF}$ and all the requests arrive before the servicing starts?