Since the points of R are found after x = 0 and x = 2, and found before x = 8, the value for x cannot start with those numbers so it would have to be either 4 or 6.
The rhombus is a square but more like a diamond shape with all equal sides. So if the difference between Q & T is (2,4), then you would have to go backwards by the same amount from (8,4)
