Exercise
Find all the solutions mod 35 to the equation 21x = 7 mod 35.
There are no solutions
The solutions for x are: 2, 7, 12, 17, 22, 27, 32
The solutions for x are: 2, 9, 16, 23, 30
The solutions for x are: 2, 13, 27, 31
Hint: 2 · 21 - 35 = gcd(21,35). How does that help you?
That is correct
That is incorrect, the solutions increase by 35/gcd(21,35)
That is nonsense