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.
['4855', 'i', '6803', 'T', 'B', 'M', '5105', '3867', '2161', '9809', '3487', '5291', 'w', '9749', '6783', '4955', '8879', 'W', 'p']