I cannot suggest anything other than the set of real numbers here, but maybe someone else can provide a better answer. As long as you increase or decrease x (which is a real number) then you will get a real number, or the infinite set of real numbers.
44 boots were sold all together. To figure this out first you need to find how many of the other boots there were. 8 rugby boots and 12 hiking boots. 8 + 12 + 24 = 44.