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.
['P', 'G', 'i', 'U', 'J', 'U', '9843', 't', '7705', 'F', 'q', 'I', 'j', '2825', 'r', 'N', '1215', 'U', 'k']