The point (3.5,−3) is the midpoint of (3,−4) and what point?

Let (x, y) be the other point.

So we have, using the mid-point formula......

(3 + x) /2 = 3.5      and   (-4 + y)/2 = -3       multipling both equations by 2 on both sides

3 + x = 7               and     -4 + y  = -6         and solving for x and y, we have

-3        -3                         +4          +4

      x = 4               and            y = -2

So the point is   (4, -2)