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.
['W', '4453', '5895', 'Z', 'A', '7663', '2749', 'f', 'H', '6917', '1215', 'M', '1775', '5397', 'l', '8197', '5209', '8229', 'U']