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.
['7759', '5735', '3565', '1101', 'D', '4133', 'k', 'n', 'l', '7929', 'z', '7223', '2019', '9781', '3827', 'I', '4523']