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.
['i', 'j', '91', 'J', '9613', '311', 'd', '531', '203', 't', '5005', 'U', '233', '8917', 'x', '1203', 'S', '6873', '4191', 'i']