Hi again,
I guess you also have to specify the problem a little more clearly too. For example, can you use four input gates or just two input gates, and does a NOT (inverter) count as one gate or can you negate an input or output any time you feel like it and not cause an addition of one more gate?
Also, when you say, "Mux", do you mean a four to one multiplexer, and does that add as one gate or do you have to construct the multiplexer with gates too?
The other mapping for the XOR is:
C=(A+B)*(A'+B')
if that helps any.