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.
['8429', 'D', '9917', '4689', 'w', '7529', '8979', 'A', 'S', '8169', 'C', '9067', 'c', '5423', 't', 'g', 'W', '6135', '3645', 'M']