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.
['513', 'K', '5745', '8203', 'f', '3377', '4899', '1683', 'T', 'K', 'd', '6445', '4801', '1173', 'k', 'q', '751', 'x']