Geometry

Question Analysis：
This question involves finding a missing coordinate using the definition of a parallelogram in the coordinate plane.
The main focus is on vector translation and opposite sides.

Key Concept Explanation：
In a parallelogram, opposite sides are equal in length and direction. So,
Vector AB must be equal to vector DC
Vector AD must be equal to vector BC

Step-by-Step Solution：
AB goes from A(1, 2) to B(5, 2), so vector AB = (4, 0)
AD goes from A(1, 2) to D(1, 6), so vector AD = (0, 4)
To find point C, apply vector AB to point D:
D(1, 6) + vector AB(4, ...