The answer is whole numbers
Because the x is the number of complete products, and we're multiplying a whole number(x) by another whole number(16) and adding a whole number (200)
This give us a whole number.
The integers includes negative numbers, and since x cannot be negative, c(x) never will be negative.
The positive real numbers includes pi, e, the square root of 2, all those numbers would never be a value of c(x)
the positive rational nubers includes 200.5, and since we're counting complete products, we'll never have fractions.
Then the set that best describes the domain are the whole numbers