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.
['K', 'u', 'P', 'R', 'R', 'L', '949', '6743', '6247', 'q', 'x', 'T', 'Y', '5923', '4155', '5633', 'r', 'K', 'U', '893']