Final answer:
The coordinate of point D, which is the midpoint of BC, is 7 when A has the coordinate -8 and C has the coordinate 12.
Step-by-step explanation:
If point A has the coordinate -8 and point C has the coordinate 12, and B is the midpoint of AC, first we need to find the coordinate of B. The midpoint formula states that the midpoint M between two points X1 and X2 is given by (X1 + X2)/2. Applying this formula, we find that the coordinate of B is (-8 + 12)/2 = 2. Since B is at 2 and C is at 12, to find the midpoint D of BC, we use the same formula: (2 + 12)/2 = 14/2 = 7. Therefore, the coordinate of D is 7.