I want to make an excess-3 adder and an excess-3 subtractor using two 4-bit binary adder (the inputs are already in exess-3) and then show the results in excess-3 on a seven segment. for example, 2+7=9 we have 0101+1010=1100(after subtracting 3 cause exess-3 + exess-3= exess-6) or for subtracting 1-8=-7 we have 0001-1011= -1010 (I should use another seven segment to show the negative) but I have trouble showing 1100 and 1010 with two seven segments. I know I should use 2 seven segments when I have 7,8 or 9 in the result but I don't know how to do that. like when I add 9 to 9 which is 1100 in excess-3 I get 1 in carry and 1011, how can I show this as 21(18 in exess-3) on the seven segments?