2(x - 3) + 4y - 2(x - y - 3) + 5 =
2x - 6 + 4y - 2x + 2y + 6 + 5 =
6y + 5 <== ur x terms cancel and ur 6's cancel
Your answer is in the picture. Hope it helps!
The unknown vertex is on the perpendicular bisector of the opposite side. So the x coordinate is the same as that of the midpoint, x=(18+52)/2=35.
Here is number 7:

Here is number 8:

Use the quadratic formula to find the other two solutions: