Instead of doing your problem for you, I'll do another one that is exactly like
it step by step.  The problem I'll do for you is this:

First I plot the points and draw the line:
  

Average the first coordinates, which are 11 and -6:
Add them (11)+(-6) = 5
Divide by 2.
Get 
So  is the first coordinate of the midpoint.

Average the second coordinates, which are -15 and 9:
Add them (-15)+(9) = -6
Divide by 2.
Get , which reduces to -3
So  is the second coordinate of the midpoint.

So  is the midpoint of the
line segment.  Let's plot it as a check.  To plot the improper
fraction , we change it to mixed number .

  

That looks like the midpoint, So I think the correct answer to the problem
I worked is



Now do your problem exactly the same way step by step.

Edwin