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.
['Z', 'U', 'R', '63', 'g', '2679', '9165', 'X', 'c', '8371', 'B', '6273', 'w', '2459', 'H', '7449', 'X', 'Q', 'P', 't']