Answer:
AC = 28
Step-by-step explanation:
Because B is the midpoint of AC, AB and BC are equal in length. You can set these equations equal to each other to find x. 7x=4x+6 -> 3x=6 -> x=2. You can plug in x to AB's equation, 7x to get 14. This represents half of AC, so multiply it by 2 and you get 28 for the length of AC. Hope this helped!