def imperial_subtract(l1, l2):
    """Subtracts one number from another in feet and inches

        Parameters
        ----------
        l1: tuple
            A length in the form (feet, inches)
        l2: tuple
            A length in the form (feet, inches)

        Returns
        -------
        ret : tuple
            Length 1 minus length 2, in (feet, inches) 
    """
    total = l1[0] * 12 + l1[1] - (l2[0] * 12 + l2[1])
    feet = total / 12
    inches = total % 12
    return feet, inches
