I have attach the circuit that I have to complete>>>>What I need know is on the adder where should I place B4,B3,B2,B1 on the comparator to have my output excess-3....the whole point of the circuit have the output on the adder to convert binary to excess-3.
Try doing a truth table for the 16 states of A1 - A4. The output should be the excess 3 code for each state. Then see what would have to be added to the unconverted data in order to produce the code. Arrange the B inputs such that the A input states make then add to produce the excess 3 code.