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.
['3843', '7761', '8011', 'T', 'o', 'A', '3989', '3457', 'N', 'v', '6487', 'V', 'i', 'o', 'H', '9899', '5997', '2589', '2839', 'K']