from typing import List


def add_rows(row1: List[float], row2: List[float]) -> List[float]:
    """
    Return the sum of the rows by adding the corresponding elements of each row.

    Preconditions:
     - len(row1) == len(row2)
    """
    return [row1[i] + row2[i] for i in range(len(row1))]