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.
['6679', '6127', 'S', 'B', '4905', 'R', 'B', '9711', '4383', '4551', '1463', 'c', '5331', '5559', '8025', '6305', '5281', 'F', 'g', '4055']