Final answer:
The question cannot be answered with the information provided, but generally, the midpoint's y-coordinate between two points can be found by averaging the y-coordinates of those two points.
Step-by-step explanation:
The question is asking for the y-coordinate of a fire extinguisher's location that is located halfway between Apartment 1 and Apartment 2. To determine this, we would need to know the y-coordinates of both apartments. However, the information provided does not include any y-coordinates but gives an example involving x-coordinates and the trajectory of a fireworks shell. With the information provided, it is not possible to determine the y-coordinate of the fire extinguisher's location. Normally, if the y-coordinates of the two apartments were given, one would simply find the average of the two y-coordinates to find the y-coordinate exactly halfway between the two points. This method is based on the concept of the midpoint in geometry, which can be calculated using the midpoint formula for a line segment in a coordinate plane.