Cooperation of Congruences and Equations.

[VoldyRoss]

I've three simple enough questions on congruences.

Obviously, if 3x=6, then x=2
And I know that if 3x≡6 mod 13, then x≡2 mod 13.


However, these one's I'm not sure of.
Please correct me if either of these three are incorrect...

1) If 3x≡6 mod 15, then x≡2 mod 15
2) If 4x≡8 mod 15, then x≡2 mod 12
3) If 4x≡8 mod 15, then x=2

Also, if they are incorrect, an explanation as to why would be greatly appreciated....

Thanks in advance....