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.
['5395', '6389', '451', 'd', 'n', 'B', 'd', '7771', 'S', 'S', 'R', '5417', '2923', '1557', 'd', 'Y', '8703', 'j', '4003', '2089']