The function is c(b) = 10b. The domain is the possible set of values
that can take the independent function, this is b. Given that b refers
to a number of boxes, which should be a non negative whole number, it
may be any natural number, this is 0, 1, 2, 3, 4, 5, ... and you can
express the domain as the set of the natural numbers. Answer: the domain
is the set of the natural numbers.