the coefficiont of x2 must be 1, so divide the equation by 3
[tex]x^2-6x=119[/tex]take half the coefficient of x and squared
[tex]\begin{gathered} \frac{-6}{2}=-3 \\ \\ (-3)^2=9 \end{gathered}[/tex]then, add to both sides
[tex]x^2-6x+9=119+9[/tex]Now we can rewrite the left side of the equation as a square term.
[tex]\begin{gathered} (x-3)^2=128 \\ \end{gathered}[/tex]