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.
['1967', '3005', 'b', '5305', '5775', 'f', '3911', 'd', 'p', '983', '3291', '6879', 'S', '5417', 'P', '5251', '9657', '5855']