Final answer:
The subject is Mathematics, focusing on functions and domain. Due to an error in the question, we cannot calculate f(-6) with the given function f(x) = 6.0 40. The domain is non-negative integers between 0 and 20, indicating that the scenario expects sales in this range.
Step-by-step explanation:
The question is from the field of Mathematics, specifically dealing with functions. The given function f(x) is meant to represent the daily profit a company makes when they sell x shirts. The function provided seems to be incomplete, possibly due to typos in the question as it only says f(x) = 6.0 40 which is not a valid function. However, considering other information provided, the function intended may be a constant function where the profit is the same regardless of the number of shirts sold. For example, if the profit was always $40, then the function would be f(x) = 40.
For the domain of the function, it is given that 0 ≤ x ≤ 20, which means the function is defined for the number of shirts sold from 0 to 20. Therefore, the domain of the function is all real numbers between and including 0 and 20. It would be inappropriate to calculate f(-6) as negative numbers of shirts don't make sense in this real-world scenario, and also because the domain is restricted to non-negative values of x.
An appropriate domain here would be to only include the non-negative integers that represent the number of shirts that can be sold, hence the domain for this function would be 0 ≤ x ≤ 20.
Considering another scenario where a realistic profit function is expected to increase as the number of shirts sold increases, the profit function might be linear or some other type where the profit per shirt increases with each additional sale. For instance, the profit might take the form f(x) = a*x + b, where a and b determine the rate of change in profit with each additional shirt sold and the basic profit when no shirts are sold, respectively.