As soon as I have studied I got that count to infinity problem will not occur if A advertise its window first to B before B can. As a result B gets information that X is un reachable now, and system will be in stable state.
Screen shot of above theory:-
Now I also know that how to solve this using split horizon i.e. B sends its routing table to A but it will not sends that row in the advertising table which contain entry which shows that "B knows the path to X which passes through A". and thus it will not send this infor to A.
But I am getting difficulty in understanding what is split horizon.
In the line saying: "Node B can still advertise the value for X......." till last line.