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.
['r', 'z', 'u', 'D', '3449', 'E', 'f', 'w', '1627', '4093', '955', 'i', 's', 'R', 'b', '9773', '2169', 'M', '9305', '4775']