From the Math 30-1 Information Bulletin 2023-2024 on the Alberta Education website, a commentary on strengths and weaknesses states that students continue to have difficulty finding the range of a rational function with a point of discontinuity. 

Collectively, the shape of the graph, the horizontal asymptote, and the y-coordinate of the point of discontinuity will provide the necessary information to make an accurate range statement.

The following link will be very helpful as a method in determining horizontal asymptotes using the degrees of the numerator and the denominator.