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.
['3735', '6723', 'Y', '165', 'P', '6121', '397', 'B', 'F', 'r', 'c', 'n', '7051', 'G', 'r', '39', '9199', '9991', 'f']