First, subtract #color(red)(8)# from each side of the inequality to isolate the #x# term while keeping the inequality balanced:

#18 - color(red)(8) <= -2x + 8 - color(red)(8)#

#10 <= -2x + 0#

#10 <= -2x#

Now, divide each side of the inequality by #color(blue)(-2)# to solve for #x# while keeping the inequality balanced. However, because we are multiplying or dividing an inequality by a negative term we must reverse the inequality:

#10/color(blue)(-2) color(red)(>=) (-2x)/color(blue)(-2)#

#-5 color(red)(>=) (color(blue)(cancel(color(black)(-2)))x)/cancel(color(blue)(-2))#

#-5 color(red)(>=) x#

To state the solution in terms of #x# we must reverse or "flip" the inequality:

#x <= -5#