#rArr##color(white)("XXXX")##2w = 9##color(white)("XXXX")#since you can add a constant to both sides of an equation without changing the validity of the equation.

#rArr##color(white)("XXXX")##w = 9/2##color(white)("XXXX")#since you can divide both sides of an equation by a non-zero constant without changing the validity of the equation.