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.
['3939', '6671', 'X', 'g', '6185', 'I', '6749', '2595', '9239', '6139', 'V', '9859', '5023', 'H', '7839', 'k', '6187', '1729', 'u']