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.
['7705', 'o', 'a', 'r', '3387', '65', '4367', '9887', '273', '3063', '4325', '4751', '193', 'U', 'a', 'F', '1569', 'L']