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.
['4271', '5085', 'j', '9591', 'u', 'z', '3037', '5867', 'P', 's', '6875', 'z', 'X', '1241', 'B', '2579', 'j', 'x', 'f', '3759']