nbde part 2 questions/doubts

[bostonian80]

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does anyone know answer to the following two radiology questions:

1. PID 16 inches and exposure time 1 sec. to maintain same density the exposure time for a film at PID 8 inches is........
2. PID 3 feet and radiation exposure 1 roentgen. radiation exposure at 6 feet is.............................

Thanks!