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.
['699', 'S', 'D', '4791', '1221', 'a', '4977', '4177', 'V', 'I', 'x', '6613', 't', 'f', 'R', '1867', '5425', 'E', '1929', '9351']