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.
['i', 'I', '6167', '4729', '4039', 'R', 'n', '4533', 'U', 'f', '4739', 'I', '521', '6109', 'Q', 'r', '2483', 'c', '3459']