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.
['1587', '6105', '5843', '1147', '1629', '6909', '6657', '9993', '7461', 'x', 'x', '6337', 'o', 'G', 'U', 'u', '569', '4737', 'f']