A sub-playbook is configured to loop with a For Each Input.

In a For Each Input loop, each iteration takes the next value from the list inputs while keeping constant inputs unchanged.

On the second iteration:

x = X (second value of W,X,Y,Z)

y = b (second value of a,b,c,d)

z = 9 (constant for all iterations).

So, the values are X, b, 9.