Throughout this answer I assume you mean -(2/3)x >= 8.

To solve this we first multiply each side by -1 and change the direction of the inequality sign:

(2/3)x <= -8

We then multiply each side by (3/2):

(3/2)(2/3)x <= -8(3/2) ==> x <= -(4*3) ==> x <= -12.

This is the final answer. If you were to show the correct interval on the x-y plane (a graph), you would draw a vertical line through x = -12 and shade the area to the left of the line.