In order to find the midpoint between two points you just need to add their coordinates and then divide the results by two:
[tex]\frac{(-9,3)+(-2,-8)}{2}=\frac{(-9-2,3-8)}{2}=\frac{(-11,-5)}{2}=(-5.5,-2.5)[/tex]Then the midpoint we are looking for is (-5.5,-2.5).