Final answer:
The most appropriate domain for the function M(x) = 6x would be whole numbers less than or equal to 100.
Step-by-step explanation:
The most appropriate domain for the function M(x) = 6x would be whole numbers less than or equal to 100. In this case, x represents the number of customers attending the movie theater, and since the capacity of the theater is 100 people, the maximum number of customers that can attend is 100. The domain of the function should reflect this limit.