Answer:
The equation of the horizontal line passing through (4, 9) will be:

Please also check the attached line graph.
Explanation:
We know that the equation of a horizontal line is always the kind of equation such as:

- As in the pint (4, 9), ordinate is 9.
- In other words, y=9
Thus, the equation of the horizontal line passing through (4, 9) will be:

Please also check the attached line graph.