7i : S ® aX, X ® Xb | l
7ii: S ® XY, X ® aX | l , Y ® bY | l
7iii: S ® baaS | aabS | l

8i:  S ® aS | baS | bbaS | b | bb | l
8ii: S ® XbXbX | XbXbXbX, X ® aX | l
8iii:  (same as b*a*) S ® XY, X ® bX | l, Y ® aY | l

Chapter 14

4i:  aⁿb²ⁿ , n = 0,1, ...
4ii: S ® aSbb | l
4iii:  no, by the pumping lemma for regular languages