Graph: 20x + 3.00y is greater than or equal to 500

Do you mind if I re-arrange it slightly before we solve it ?

         You said     20x  +  3.00y  ≥  500

Subtract  20x
from each side:               3.00 y  ≥  -20x + 500

Divide each side by  3 :          y  ≥  -20/3 x  +  500/3

Make it an equation,
and graph this line:                  y  =  -20/3 x  +  500/3

The line is made out of all points where 'y' is EQUAL to
1/3 of (-20x + 500).

The inequality wants to see all the points that are equal to it
AND all the points that are greater than that.

So the graph of the inequality is the line AND every point that's
anywhere above the line.  It's called the "half-infinite plane"
bounded by the line.