X=6, AC=12.
Since it is the midpoint, B splits AC down the middle, meaning that AB and BC are equal. Set them equal, so your equation should look like this: 2x-7=5. Add 7 to both sides, then divide by 2 and you should get x=6.
To find AC, just add 6+6 since both sides are equal to get 12.
Hope this helps!
