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.
['5459', '8555', '7415', '9243', '3305', '1347', 'R', 'y', 'h', '8305', 'k', 's', '259', '4955', '4653', 'M', 'l', '5455', '3633', '179']