You can do it like this. Subtract the right side. Expand parentheses. Collect terms. Divide by the coefficient of x. Add the opposite of the constant term.
3(2x -3) -9x -4 -(2x +12) = 0 . . . . . . subtract the right side
6x -9 -9x -4 -2x -12 = 0 . . . . . . . . . .eliminate parentheses
x(6 -9 -2) -(9 +4 +12) = 0 . . . . . . . . . collect terms
-5x -25 = 0 . . . . . . . . . . . . . . . . . . . . finish collecting terms
x +5 = 0 . . . . . . . . . . . . . . . . . . . . . . . divide by the coefficient of x
x = -5 . . . . . . . . . . . . . . . . . . . . . . . . . add the opposite of the constant
These general instructions will work for any single-variable linear equation.