This problem is really easy. You set up the first coordinate and then the midpoint on the bottom
(-9 , -6)
(7 , 2)
Now there are 16 steps from -9 to 7, then you add 16 more to 7 and you get 23 for the x axis.
There are 8 steps from -6 to 2, now count 8 more steps, and you get 10 for the y axis.
The coordinates of C are (23 , 10)
Hope it helped!