\[x^{2} - 7x + 12 = (x - 3)(x - 4)\]
\[x^{2} - 7x + 12 = 0\]
\[x_{1} + x_{2} = 7;\ \ x_{1} \cdot x_{2} = 12\]
\[x_{1} = 3;\ \ x_{2} = 4.\]