20x - 3(7x + 6) <(=) -8x + 16
distribute on the left 20x - 21x - 18 <= -8x + 16
combine like terms on the left
-x - 18 <= -8x + 16
add 8x to both sides
7x - 18 <= 16
add 18 to both sides 7x <= 34
divide both sides by 7 x<= 34/7
set builder notation is {x\ x <= 34/7}