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.
['6499', 'Z', 'm', '9583', '1011', 'A', '3493', 'y', '6183', '2377', '4069', 'R', 'K', 'z', '5497', '1441', 'V', 'u', 'j']