First, we distribute the #color(red)(3/4)# term across each of the terms within the parenthesis:
#(color(red)(3)/color(red)(4) xx 4x) + (color(red)(3)/color(red)(4) xx 8) = -12#
#(color(red)(3)/cancel(color(red)(4)) xx color(red)(cancel(color(black)(4)))x) + (color(red)(3)/cancel(color(red)(4)) xx color(red)(cancel(color(black)(8)))2) = -12#
#3x + 6 = -12#
Next, subtract #color(red)(6)# from each side of the equation to isolate the #x# term while keeping the equation balanced:
#3x + 6 - color(red)(6) = -12 - color(red)(6)#
#3x + 0 = -18#
#3x = -18#
Now, divide each side of the equation by #color(red)(3)# to solve for #x# while keeping the equation balanced:
#(3x)/color(red)(3) = -18/color(red)(3)#
#(color(red)(cancel(color(black)(3)))x)/cancel(color(red)(3)) = -6#
#x = -6#