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: ['8109', '5635', 'u', 'M', '1009']

SOLUTION: 14753

PROBLEM: ['R', 'J', 'z', 'o', '1121', '7247', '8987', 'u']

SOLUTION: 17355

PROBLEM: ['M', '543']

SOLUTION:
543