I want to make an exess-3 adder and an exess-3 subtractor using two 4 bit binary adder and then show the results in exess-3 on a seven segment. I know I should use 2 seven segments when i have 7-9 in the result but I don't know how to do. like when I add 9 to 9 which is 1100 in exess-3 I get 1 in carry and 1011, how can I show this as 21 on the seven segments ??