NOTE: I didn't check if the answers for b, c, and d were correct. just for the things I mentioned above.
Other solutions include:
[1011] (W=1, X=1), [1110] (W=1, X=0), [0101] (W=0, X=1), [1001] (W=0)
[1011] (W=1, X=1), [1110] (W=1, X=0), [0101] (W=0, X=1), [1010] (W=0)
[1011] (W=1, X=1), [1010] (W=0, X=0), [0101] (W=0, X=1), [1101] (W=1)
[1011] (W=1, X=1), [1010] (W=0, X=0), [0101] (W=0, X=1), [1110] (W=1)
[1011] (W=1, X=1), [1101] (W=1, X=0), [0110] (W=0, X=1), [1001] (W=0)
[1011] (W=1, X=1), [1101] (W=1, X=0), [0110] (W=0, X=1), [1010] (W=0)