Answer:
I'm not sure if this is correct but this is how i do it.
Explanation:
I take the distance between two points first.
Then, I divide it by two to get it's half length.
Then, I take the lowest point of the two which is (3,5).
Then, I add 2 to 3 and 4 to 5 which makes it (5,9).
Again, this is how I usually do it. I hope others will also answer your question.