Math Problem, graphing systems of inequalities/linear programming?

Please just read it, I have done a majority of the work. I just need help on one thing.
And I put all this so someone can correct me if I’m wrong.. Please help.

A construction employs two levels of tile installers: craftsmen and apprentices. Craftsmen install 500 square feet of specialty tile, 100 square feet of plain tile, and 100 linear feet of trim in one day. An apprentice installs 100 square feet of specialty tile, 200 square feet of plain tile, and 100 linear feet of trim in one day. The firm has a one-day job that requires 2000 square feet of specialty tile, 1600 square feet of plain tile, and 1200 linear feet of trim in one day. The construction firm pays craftsmen $200 per day and pays apprentices $120 per day. How many craftsmen and apprentices should be assigned to this job so that it can be completed in one day with the minimum labor cost? What is the minimum labor cost?
Let x represent the number of craftsmen and let y represent the number of apprentices.
Write a system of 5 inequalities to represent the constraints.
Graph the feasible region and clearly label the four corner points.
Write an objective function for the labor costs.

I already have the five inequalities.
500x+100y≥2000 —> y≥-5x+20
100x+200y≥1600 —> y≥-1/2x+8
100x+100y≥1200 —> y≥-1/4x=12
x≥0
y≥0
The objective function.
And my graph, http://s158.photobucket.com/albums/t109/inot123/?action=view&current=Graph_paper2.gif
(Sorry it didn’t upload good…)
I don’t know what the four corner points on the feasible region are. Help please.
mominsd- thank you. When I first did the equation I put 100x+100y and solved it from there. Thank so much.
Still kind of confused though.. :/
Thank you so so so so much.

Your 3rd inequality– 100x+100y≥1200 —> y≥-1/4x=12

100x + 100y ≥ 1200 is correct, but it simplies to:
y ≥ -x + 12

Hopefully that will help you find your corner points?

Edit:
Ok, I found this site: http://www.walterzorn.com/grapher/grapher_e.htm

In the section where you plug stuff in, copy and paste this:

-5x+20;
-.5x+8;
-x+12

And I set the x and y mins to -5, x and y max to 25
That will give you the graph.

Now, your feasible region.
(0,20) and (16,0) are the two obvious points.
(2,10) is where y≥-5x+20 and y ≥ -x + 12 intersect.
(8,4) is where y ≥ -x + 12 and y≥-1/2x+8 intersect.

So those are the corner points. Hope that helps!