we have the inequality
1/3x -8 >=x+6
solve for x
Multiply by 3 both sides
x-24 >=3x+18
-24-18 >=3x-x
-42 >=2x
divide by 2 both sides
-21 >=x
Rewrite
x <= -21
so
the solution is the interval (-infinite, -21}
In a number line the solution is the shaded area at left of the number -21 (close circle)
therefore
the solution in the attached figure