elementary number theory - Linear diophantine equation $100x - 23y = -19$

I need help with this equation: $$100x - 23y = -19.$$ When I plug this into Wolfram|Alpha, one of the integer solutions is $x = 23n + 12$ where $n$ is a subset of all the integers, but I can't seem to figure out how they got to that answer.

Answer

$100x -23y = -19$ if and only if $23y = 100x+19$, if and only if $100x+19$ is divisible by $23$. Using modular arithmetic, you have
$$\begin{align*}
100x + 19\equiv 0\pmod{23}&\Longleftrightarrow 100x\equiv -19\pmod{23}\\
&\Longleftrightarrow 8x \equiv 4\pmod{23}\\
&\Longleftrightarrow 2x\equiv 1\pmod{23}\\

&\Longleftrightarrow x\equiv 12\pmod{23}.
\end{align*}$$
so $x=12+23n$ for some integer $n$.