See attached file for full problem description.
This solution is comprised of a detailed explanation for solving the problems on polynomial congruences.
It contains step-by-step explanation for finding all solutions of each of the following congruences:
(a) x2 + x +1 ≡ 0 (mod 11)
(b) x3 + x + 1 ≡ 0 (mod 13)
(c) x4 + x3 + 2 ≡ 0 (mod 7)
Solution contains detailed step-by-step explanation.