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.
['s', 'G', 'w', '6445', '8545', '8829', 'Z', 'W', 'Z', '3201', 'k', '1341', 't', 'k', 'U', 'f', '1931', 'u', '8511']