from typing import List
from functools import reduce


def sum_dictionaries(dicts: List):
    """
    Sums the values of the common keys in dictionary.

    Parameters
    ----------
    dicts (list) dictionaries containing numeric values

    Returns
    -------
    dictionary with summed values
    """

    def reducer(accumulator, element):
        for key, value in element.items():
            accumulator[key] = accumulator.get(key, 0) + value
        return accumulator

    return reduce(reducer, dicts, {})