For = {x, y}, use finite languages from * (as in Example 6.12), together with set

Question:

For ∈ = {x, y}, use finite languages from ∑* (as in Example 6.12), together with set operations, to describe the set of strings in ∑* that
(a) Contain exactly one occurrence of x;
(b) Contain exactly two occurrences of x;
(c) Begin with x;
(d) End in yxy;
(e) Begin with x or end in yxy or both;
(f) Begin with x or end in yxy but not both.