use the method of example 9.5.10 to answer the following questions. (a) how many 14-bit strings contain exactly six 1's? the number of 14-bit strings that contain exactly six 1's equals the number of ways to choose the positions for the 1's in the string, namely, . (b) how many 14-bit strings contain at least eleven 1's? (c) how many 14-bit strings contain at least one 1? (d) how many 14-bit strings contain at most one 1?