Question

What are the coordinates of the fourth point that could be connected with (–8, 0), (1, 0), and (1, –5) to form a rectangle?

Answer 1

(-8, -5)

To form a rectangle, all the lines must be perpendicular and parallel. If you draw out the points on a coordinate plane then you can find the answer pretty easily. 

Also, this one is easy because all the lines are vertical or horizontal, and when that is the case then you can just see which number in the set hasn't appeared twice (1 appeared twice as an x value, 0 appeared twice as a y value, but -8 has only appeared once as an x and -5 has only appeared once as a y value)