the midpoint formula ought to work easily enough.
You can simply say....
the x co-ordinate of the midpoint is halfway between the x co-ordinates
of the points on the line.
So -2 is halfway between 7 and another x.
-2 is 9 away from 7.
The other value 9 away from -2 is -11.
So -2 is halfway between -11 and 9.
Also 4 is halfway between 10 and -2
The other point is (-11,-2).
Using the midpoint formula, which is
"the x midpoint is the average of the x values"
"the y midpoint is the average of the y values".