Problem with a sheet metal flange

Need some help. I have a sheet metal flange that when bent in solidworks, the lower corner intersects the bottom flange. I'd like to have it cut back where it is parallel with the bottom flange but am having trouble making this happen. I cant seem to sketch a triangle and extrude a cut...solidworks won't let me do that.

Any other suggestions?

-Mark

SolidworksSheet Metal