OpenGL School Project Arch simple rectangle with transparent half-circle need help ASAP

http://img503.imageshack.us/my.php?image=clipimage002yr3.jpg

The image above is essentially what I must draw with my openGL program.
This is for a school project, and I am not doing very well so if I mess this up I am resigned to a grim fate.
I'm pretty confident that I could handle everything *BUT* the notch in the block as simple as it looks. I know maybe this has something to do with transparency but I feel clueless right now. If anyone has any idea how I could do the notch in the block to make an 'arch' please let me know. I have only a few days left to figuere this out or I am dead meat.
lordvrAsked:
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InteractiveMindCommented:
Does it have to use transparency?
It would seem simpler to just draw a polygon - defining the arc yourself; (with a little bit of pythag, that shouldn't be particularly difficult)..
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InteractiveMindCommented:
Try

float W=200, H=100, ar=50; // W is the width of the rectangle (which contains the arc),
                                              // H is the height of the rectangle (..)
                                              // ar is the radius of the arc
glBegin(GL_POLYGON);
glVertex3f(-W/2,0,0);
glVertex3f(-W/2,H,0);
glVertex3f(W/2,H,0);
glVertex3f(W/2,0,0);
for(float i=ar; i>=-ar; i--)
{
    gl.glVertex3f(i,(float)sqrt(ar*ar-i*i),0);
}
gl.glEnd();
0

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