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: ['P', '6299', '9655', 'l', '6317', '2139', '3347', 'l', '3095', '7363', '3115', '7529', 'R']

SOLUTION: 48859

PROBLEM: ['2087', '8171', 'c', 'd', 'a', '5621', 'n']

SOLUTION: 15879

PROBLEM: ['U', 'u', '1559', 'k', 'A', 'D', '5283']

SOLUTION:
6842