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.
['u', '1577', '4581', '5255', '9895', '3209', 'T', '437', '8795', 'V', 'o', 'K', 'n', 'U', '7785', '3381', 'S', '2575']