Final answer:
The driver will require 5 polls to detect that the device is no longer busy, as the fifth poll at 45 use c will occur after the device completes its 42-usec operation.
Step-by-step explanation:
If a driver polls its associated device every 9 microseconds (usec), and the device takes 42 microseconds to complete its operation, we can calculate the number of polls required to detect when the device is no longer busy. The device is busy for 42 microseconds, so the first poll happens at 9 microseconds, the second at 18 microseconds, and so forth. After each poll, the driver must wait another 9 microseconds before the next poll.
To cover the operation time of 42 microseconds, the driver would have polled at 9, 18, 27, and 36 microseconds. The fifth poll occurs at 45 microseconds, after the operation has completed. Therefore, it is at the fifth poll that the driver would detect the device is no longer busy.