The sum of 5 and the twice a number is at most 27

If you are looking to write an inequality equation that models this situation, then the answer would be: .  The "at most" signals to use the less than or equal to sign.

No, not every function will have a hole. This is considered a special case.          A typical function is one that can be written as a fraction of two polynomials where the denominator is not zero. In a special case (when there is a hole), a factor may appear in both the numerator and denominator.