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.

['r', '6537', '3001', '7879']
17417

['4701', 'b', 'i', 'B', 'z', '7837', 'W']
12538

['o', 'p', 'f', '2689', 'e', '6737', '2273', '3781', '4821']

20301