The inorder traversal of the nodes are
10,30,40,50,70,90,120,150,175
But in order to get 50 after traversing all the nodes 10,20,30 should be in this order and
70,90,120,150,175 should be in the this order only .
Therefore 8! / (3! * 5!) = 56 (10,20,30 remains in this order always so divide by 3! and 70,90,120,150,175 remains in this order always so divide by 5! ).
Ans 56.
