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.
['3751', 'b', '3989', 'v', '4553', 'p', '7953', '5555', 'j', '2895', 'Z', '5689', '179', '9221', '8979', '897', 'm', '7493']