Answer
D
Work Step by Step
To find the coordinate of the midpoint, first find the length of $\overline{AG}$.
AG=$|-3-3|=|-6|=6$
Since AG=6, the midpoint is half way between, or 3 units from, each endpoint.
One endpoint is -3, so:
Midpoint=$-3+3=0$
The coordinate of D is 0, so D is the midpoint.
