First, expand the terms within the parenthesis by multiplying each term within the parenthesis by the term outside the parenthesis:
#161 = 4x + color(red)(3)(3x + 19)#
#161 = 4x + (color(red)(3) xx 3x) + (color(red)(3) xx 19)#
#161 = 4x + 9x + 57#
#161 = (4 + 9)x + 57#
#161 = 13x + 57#
Next, subtract #color(red)(57)# from each side of the equation to isolate the #x# term while keeping the equation balanced:
#161 - color(red)(57) = 13x + 57 - color(red)(57)#
#104 = 13x + 0#
#104 = 13x#
Now, divide each side of the equation by #color(red)(13)# to solve for #x# while keeping the equation balanced:
#104/color(red)(13) = (13x)/color(red)(13)#
#8 = (color(red)(cancel(color(black)(13)))x)/cancel(color(red)(13))#
#8 = x#
#x = 8#