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.
['3149', '4063', 'H', 'R', '5575', '7265', '1871', 'i', 'y', 'S', 'K', 'S', 'i', 'y', '811', 'P', 'Z', 'Q', 'M']