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.
['7923', 'F', 'V', 'k', 'g', 'g', 'q', '9979', '831', 'H', '6471', 'c', '1285', '5281', 'r', '7419', '5697', '8955', 'E', '525']