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', '9905', '7473', '7795', 'A', '5521', '5907', '2589', 'q', 'W', '9749', 'q', '4235', '4177', 'F', 'c', 's', '2457', 'N', 'u']