Answer: (b) all positive integers
Explanation:
We know that the domain of a function is the set of all values for x (independent variable) for which the function must be defined.
Given: A package of paper towels contains 3 rolls. Each package of paper towels costs $2.79.
A function, f(x), is written to represent the cost of purchasing x packages of paper towels.
i.e. the number of towels must be a positive integer .
Hence, the practical domain for the function f(x) must be all positive integers.