AutoCad 3D :: How To Remove Part Of Solid That Enclosed Within Green Surfaces

I've just started learning AutoCAD and came across my first obstacle I don't know how to work around. Here's what I'm trying to do.

I draw two lines and two circles and then trim the excessive parts as in the picture (in general it can be an area composed of various types of lines, straight lines, arc, and likely with rounded corners).

Then extrude to the height 2. This makes 4 surfaces (green). Now I build a solid 'around' the surfaces. In this example I draw a rectangle and extrude to the height 1 (red). And my question is: how do I remove the part of the solid that's enclosed within the green surfaces? Subtraction doesn't work as I don't subtract solid. Slicing doesn't work either as it's more than one surfaces. For the same reason I can't turn it into a solid.

acad02.jpg