state q0 denotes even no of a's and state q1 denotes odd no of a's.
Here we consider even no of a's then b and c should be equall.
at state q1 (c,b/$\epsilon$) //pop 'b' for one 'c'.
at state q2 also same pop 'b' for one 'c'.
If a's are odd then no restriction on a's and b's.
at state q4 'b's are pushed into the stack.
when (c,b/cb) push 'c' into stack or (c,b/b) skip 'b's.
same as q5 also.
Hence W=cb or b,X=$\epsilon$,Y=$\epsilon$,Z=cb or b