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.
['u', 'o', '4751', 'M', 'T', '7671', '5551', 'w', '4311', '9673', 'p', '6751', '4133', 'R', '177', '1523', 'S', '5345']