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.
['1651', 'y', 'M', '2313', 'w', 'j', 'T', 'R', '7671', 'Z', '4461', '7883', '2275', 'C', '391', 'o', 'y', '5757', 'U']