Problem:
Find a complete set of mutually incongruent solutions of each of the following:
(a) 7x is congruent to 5 (mod 11)
(b) 8x is congruent to 10 (mod 30)
(c) 9x is congruent to 12 (mod 15)
Provide complete and step by step solution for the question and show calculations and use formulas.