It appears that you have some boundary lines:
y = 0 (also known as the x-axis!)
y=x (a line passing through the Origin, slope of 1)
x=4 (a vertical line passing through 4 on the x-axis)
What shape is THAT? Did you say triangle? you should be able to take it from here!
There are a couple of other letters floating around in your statement of problem, but those should be ignored.