Answer:
y = 4
Step-by-step explanation:
Note that A and B have the same x-coordinate: 1. This means that AB is a vertical line through x = 1. The perpendicular bisector of AB must be a horizontal line situated halfway between y = 3 and y = 5. Thus, it's just y = 4.
Review: y = 4 bisects AB and represents a horizontal line.
