def eval_basic_op(l: str, op: str, r: str) -> str:
    """
    Evaluate a basic arithmetic operation
    :param l: Left operand
    :param op: Operator
    :param r: Right operand
    :return: Result or a string representing the operation if it cannot be calculated
    """
    if l.isdecimal() and r.isdecimal():
        l_num = int(l)
        r_num = int(r)
        if op == '+':
            return str(l_num + r_num)
        if op == '-':
            return str(l_num - r_num)
        if op == '*':
            return str(l_num * r_num)

    return l + op + r