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.
['5399', '229', '4125', 'U', 'j', '2541', '4457', 'X', '999', 'e', 'U', '6619', 'V', 'H', 'R', 'j', 'N', 'q', 'H', 'R']