The table below shows the total number of brake pads produced by machines throughout a 12-hour work day.

To find the unit rate for brake pads produced per hour, we divide the total number of brake pads produced by the number of hours.

For 3 hours: 48 brake pads / 3 hours = 16 brake pads per hour
For 6 hours: 96 brake pads / 6 hours = 16 brake pads per hour
For 9 hours: 144 brake pads / 9 hours = 16 brake pads per hour
For 12 hours: 192 brake pads / 12 hours = 16 brake pads per hour

Therefore, the unit rate for brake pads produced per hour is 16 brake pads per hour.

The answer is D. 16 brake pads per hour.