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.
['2413', '5479', '6259', 'R', '3239', 'M', 'm', 'l', 'A', '3477', 'U', '4455', 't', 'q', 'W', 'o', 'w', '5801']