In this task, you are given an input list A. You need to find all the elements of the list that are numbers and calculate their sum.
['k', 'K', 'm', 'I', 'g', 'l', 'r', 'G', '8501', 'y', '7587', '1797', '6939', '7581', 'X', 'x', 'j', '3671']