I need to turn my $4$ bit full adder into an adder$/$subtractor using multiplexers and inverters. I am trying to draw the schematic for the adder$/$subtractor$,$ but instead of having the boxes in the schematic the say "Full Adder", I want to include my $4$ bit adder as shown in the picture so that it will be easier to understand and wire up later on$.$ Please combine the two by drawing a new image. No code please.