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.
['O', 'j', 'Z', 'u', '7427', '4225', '3139', '9993', '9945', '3639', 'h', 'j', 'f', '6511', 'e', '4607', '2741', '4743']