/sci/ - Science & Math

Here's my assignment: Design a combinational circuit that adds two 4 bits binary numbers together.

Steps given to design a combinational circuit:
1. determine # of inputs and outputs
2. derive truth table to get the relationship between input and output
3. obtain a simplified boolean function for each output
4. draw a logic diagram

So I'm guess there's going to be 9 inputs and 5 outputs. Right now I'm specifically wondering if I have to make a truth table for all the 9 inputs and outputs. And if not, can someone give me some suggestion on what to do? I'm completely lost.