In this task, you are given two lists A,B. Find the longest common subsequence in the lists A and B.
['B', 'P', '9811', '9755', 'L', '2115', 'r', 'e', 'k', 'e', 6927, 639], ['u', 'k', 8553, 't', '9811', '9755', 'L', '2115', 'r', 'X', 'p', 'f', 'R']