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.
['5689', 'j', 'K', 'i', 'U', 'l', 'B', 'a', 'I', '3235', '9289', 'M', 'F', '7789', '8733', '5477', 'F', '1719', '5491']