The midpoint between two points is the midpoint that is exactly at the same distance from both points. Given two points of the form (a,b) and (c,d) we can calculate the midpoint with the formula
In our case, a=3, b= -1, c = -9, d = 8. So if we replace this values in our equation we get
So the midpoint between (3,-1) and (-9,8) is (-3, 7/2).