Find CFGs for the following languages over the alphabet = {a b}: (i) All words in

Find CFGs for the following languages over the alphabet Σ = {a b}:
(i) All words in which the letter b is never tripled.
(ii) All words that have exactly two or three b's.
(iii) All words that do not have the substring ab.
(iv) All words that do not have the substring baa.
(v) All words that have different first and last letters:

{ab ba aab abb baa bba . . . }