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.
['c', '7415', '6253', '4477', 't', '9449', '7733', '2325', 'Z', '5413', 'q', 'm', 'R', '8619', '7289', '857', '7273', '7425']