I have the following linear programming model:

Constraints:

The constraint I'm struggling with is the last one (about x's maximum value).

I've been taught to solve them by plotting the points. When you plot the points, the x value is always greater than 500 (in this case, 600,800 and 1200).

What is the appropriate course of action here? Do I just assume is 500, or do I need to do something else?

Thank you in advance