TASK DEFINITION: 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.
PROBLEM: ['3873', 'D', 'J', '2799', 'k', 'F', 'I', '3457', '5647', '4815', '7509', 'Y', '1251', '2211']

SOLUTION: 31562

PROBLEM: ['W', 'H', 'k', 'L', '2425']

SOLUTION: 2425

PROBLEM: ['u', '417', 'A', 'K', 'O', 'n']

SOLUTION:
417