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.
['1149', '6329', 'P', 'M', 'H', '8905', '9669', '1903', '6399', '5707', 'n', '6119', '8403', '943', 'i', 'o', '129', '4925', '7129', 't']