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.
['1547', '623', '6025', 'n', 'S', 'y', 'p', 'u', 'Z', '1969', 'u', 'S', '3143', '3917', '2507', 'v', '4361', '7775', 'f', '8021']