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.
['1825', 'I', '687', '6537', 't', '5493', 'i', '2387', 'x', 't', '6753', '8817', '1869', 'f', 'a', '341', '5171', 'r', 'r']