def subtract_matrices(a, b):
    """
      Subtracts matrix b from matrix a aka (a-b)

      Args:
        a: matrix to subtract from
        b: matrix to subtract away from a

      Returns:
        m: resulting matrix from a-b
    """
    m = []
    # Loop through each spot and subtract the values from eachother before adding to m.
    for row_index, row in enumerate(a):
        new_row = []
        for col_index, col in enumerate(b):
            new_row.append(a[row_index][col_index] - b[row_index][col_index])
        m.append(new_row)
    return m