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.
['p', '2643', '767', 'v', 'L', 'R', '3195', '8655', '6619', 'g', 'h', '7961', 'w', 'c', '2381', '7785', '4243', '6785']