A bit string is a sequence of zeros and ones. How many bit strings of length
11 can be constructed in each of the following cases?
(a) The strings contain exactly 7 zeros.
(b) The strings contain the sequence 10110.
(c) The strings begin with 010 or end with 110.
(d) The strings begin with 010 and end with 110, and do not contain the sequence 1111.