Q19

Suppose a disk has $201$ cylinders, numbered from $0$ to $200$. At some time the disk arm is at cylinder $100$, and there is a queue of disk access requests for cylinders $30, 85, 90, 100, 105, 110, 135$ and $145$. If Shortest-Seek Time First (SSTF) is being used for scheduling the disk access, the request for cylinder $90$ is serviced after servicing ____________ number of requests.