The midpoint of ab ab is at (3,7) (3,7) and a a is at (0,−5) (0,−5) . where is b b located

I believe the answer is (6, 29)  

The reasoning for this is the slope for (0,-5) and (3,7) is:
7+5/ 3-0  
12/3

So if we start at (3,7) and move the x over 3 it will be at 6
and if we move the 7 over 12 it will be at 29
thus the answer should be (6,29)

Hope this answer helps!