Find all x ∈ Z satisfying each of the following equations.

(a) 3x ≡ 2 (mod 7)
(b) 5x + 1 ≡ 13 (mod 23)
(c) 5x + 1 ≡ 13 (mod 26)
(d) 9x ≡ 3 (mod 5)
(e) 5x ≡ 1 (mod 6)
(f) 3x ≡ 1 (mod 6)