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.
['l', 'j', 'I', '5603', '2415', 'P', '1469', '3147', 'M', 'n', 'O', 'q', '3975', '9467', '4669', '735', 'Q', 'V']