Final answer:
When reporting time in feet and frames for 16mm film at a rate of 40 frames per foot, both feet and frames are used as units of measurement. Feet represent the length of the film, and frames represent individual images within that length.
Step-by-step explanation:
The unit of measurement used to report time in feet and frames assuming a frame rate of 16mm film being 40 frames per foot for output to 16mm film is both feet and frames. These units allow for precision when editing or projecting film, where one foot of film contains 40 frames. Therefore, to specify the amount of film used or the duration in frames, one would use the units of feet or frames respectively. Seconds and minutes are also used to represent time in film, but typically get converted from the feet and frames measurement based on the frame rate for practical viewing purposes.