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.
['3345', 'Q', 'c', 'R', '9403', '9189', 'm', 'N', '6957', 't', '613', 'N', 'q', 'p', '4833', '1539', '8451', '9885', '941', '8749']