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.
['695', 'A', '2029', '8673', 'G', 'J', 'a', '7121', 't', '3259', 'U', '9843', 'C', 'J', 'D', 'm', 'P', 'S', '155', 'R']