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.
['4015', 'F', '8835', '9527', 'v', 'k', '5217', '7653', 'l', '9889', '5337', 'H', 'V', 't', '7121', '8339', 'k', '6601']