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.
['L', '6217', 'q', 't', '9553', 'n', 'c', 'n', '7863', 's', 'r', 'X', 'f', 'w', '6273', 'd', '1791', '6209', '8843']