Answer:
When we have a function f(x), the domain of the function is the set of all the inputs that "work" (Not only in a mathematical way, the context is also important) with the function f(x)
In this case, we have a function M(p) = $2*p
This function represents the amount of money collected depending on the number of people who ride on the ferris whell.
Then p can be only a whole number (we can not have 1.5 people, only whole numbers of people).
And we also know that the maximum capacity of the ferris is 64 people.
Then:
p ≤ 64
And we also should add the restriction:
0 ≤ p ≤ 64
(Because p can't be smaller than zero)
Such that p should also be an integer, then, the domain is:
D: p ∈ Z, p ∈ {0, 1, 2, ..., 64}