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.
['w', 'W', 'I', 'f', 'f', '7841', '3651', 'r', '3287', 'v', '1107', 'V', '5245', 'M', 'j', 'T', 'W', 'W', 'g', 't']