The daily expenses for each of a transportation service company's trucks is given by the function d (x) = 15 + 0.5x, where d (x) is the daily expense per truck (in dollars) and x is the daily mileage. The input for the function includes

The input for this function must include all real numbers. We know this because the numbers that can represent the daily expense per truck variable are real numbers mainly because they need to be expressed in dollars. The same happens with x which is the daily mileage. It is expected that the amount of this variabe is expressed in real numbers