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.
['Q', '6269', 'V', 'n', '7759', 'q', '2183', 'V', 'W', '6811', 'R', 'W', '4809', '9353', 'f', 'c', '4979', 'r', '3729', 'Q']