~asap offering 15 points~ 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 a) all fractions b) all integers c) all real numbers d) all positive real numbers

The function only makes sense for
  D) All positive real numbers


It also makes sense for x=0, which would make the domain "all non-negative real numbers." However, that is not a choice.

As shown, the function is defined for all real numbers, which includes all fractions and all integers. However, in the real world, you won't be driving the truck a negative number of miles and you won't be charged less than $15 per day. So, in the real world, the practical domain of the function is as described above.