In this scenario, Joanna can have a minimum of 0 passengers and a maximum of 20 passengers on her tour bus. This means that the number of passengers can range from 0 to 20. Therefore, the reasonable domain for the number of passengers (x) is {0, 1, 2, ..., 20}.
However, since that exact set isn't provided among the options, let's analyze the available choices:
a) {0,1,2,3,4,5,6,7,8,9,10} - This is not the correct domain because it only includes numbers up to 10, while Joanna can have up to 20 passengers.
b) {15,30,45,60,75,90,105,120,135,150} - This is not appropriate as these numbers seem to be multiples of 15, not a count of passengers.
c) 0 < x < 10 - This is not correct either, as it excludes both 0 and any numbers above 10, limiting the range of possible passengers.
d) {1,15,2,3,30,3,45,4,60,5,75,6,90} - This doesn't make sense within the context of counting passengers, as it does not neatly represent a reasonable count of passengers in the bus.
Given these options, none adequately represents the domain of possible passenger counts — a better option would be {0, 1, 2, ..., 20} — but since this doesn't exist in the choices, the closest to a correct approach focusing on lower values is option a, albeit incomplete.
So the answer is none of the given options correctly represents a reasonable domain. However, if forced to choose, option (a) is the least incorrect, even though it doesn't account for all possible passenger counts.