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.
['9783', '433', '9967', '3743', '9905', '3759', '335', 'P', 'd', '9925', 'd', '5209', '2685', '4585', '7129', '1899', '6655', 'n', '6099']