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.
['q', 'S', 'X', '6897', '1755', '8967', 'O', 'X', 'w', '4919', 'b', 'C', 'B', 'Q', '1377', 'K', 't', '4253', 'x', '1845']