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.
['Q', 'g', '4675', 'I', '4797', '8411', '8219', '5805', 'y', '9665', 'M', '6439', '6061', 'u', '839', 'Y', '6439', '7667', 'S', 'V']