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.
['5023', '8439', '7847', '3553', 'B', 'm', 'z', '7713', 'i', '5787', '9493', 'P', '4603', 'U', '5885', 'l', '7181', '4303', 'v', '251']