Answer:
28
Explanation:
Since B is the midpoint of AC, that means AB = BC. That means 3x+4 = 5x-6. We can now set up an equation to solve for x:
3x+4 = 5x-6
3x+10 = 5x
10 = 2x
x = 5
Now that we know what x is, we can just plug x into the expression of AB and multiply it by 2:
(3*(5)+4)*2
=(15+4)*2
=19*2
=28
(side note: we could have plugged x into the expression of BC as well, but in this case plugging it into AB tends to be easier to solve)
Therefore, the length of AC is 28.