the set of hexadecimal digits consisting of from one through four digits can be thought of as broken up into disjoint subsets: s1, s2, and so forth, where each sk consists of the strings with k hexadecimal digits. there are $ incorrect: your answer is incorrect. strings in s1, $ incorrect: your answer is incorrect. strings in s2, and so forth. thus, by the addition correct: your answer is correct. rule, the total number of strings is .'