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.
['F', 'o', '1115', 'I', '4357', 'o', 'm', '7541', 's', '7287', 'z', 'a', '897', '7551', 'L', 'W', '2207', '5283']