1 's complement of 1101=0010 2's complement of 1101=0010+1=0011 and 1 's complement of 0100=1011 2's complement of 0100=1011+1=1100 Addition both 4 bits :
0011
+1100
────
1111
It's one's complement =0000 and 2′ s complement =0000+1=0001 There is no overflow.