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.
['4893', '8855', '7789', '2983', 'u', 'R', 'H', '8969', '4515', 'U', 'k', 'P', '8293', '375', '6895', 'n', 'z', '9651']