To find the midpoint of any two points, simply take the average of the x's and then the average of the y's. This will create a point directly in between them. To take an average, add the points together and then divide by 2. We'll start with the x values.
11 + - 7 = 4
4/2 = 2
Next we do the same for the y value.
3 + 13 = 16
16/2 = 8
Now we can take these two answers and put them together for the ordered pair of (2, 8)