Pretend that your ≤ here is just a plain old =. Balance it like you always would :)
4x+8≤6x−20 Subtract 6x from both sides
−2x+8≤−20 Subtract 8 from both sides
−2x≤−28 Divide both sides by −2 and do not forget to flip the sign because you're dividing by a negative number!
x≥14