3d form block

This is probably a pretty simple task for most. For theattached assembly, I would like to know how to cut away the surfaceof red part into the blue block. I have tried offset surfaces andtrimming with no success. This is most likely due to the fact thepart doesn't run all the way through the block. Need some helpplease! Basically trying to create a 3d form block.SolidworksSurfacing