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.
['y', '7519', '7099', '9131', 'z', 'P', 'o', '6145', 'P', 'f', '9569', '9309', 'Q', '6115', '285', '8743', 'l', 'V', 'U']