If B is the midpoint, AB and BC must be of equal length.
12x-12=4x+28
Subtract 4x from both sides
8x-12= 28
Add 12 to both sides
8x= 40
Divide both sides by 8
x=5 <======
Now plug in this value of x
12(5)-12= 60-12 = 48 <========
4(5)+28= 20+28= 48 <=======
Add the values to get AC
48+48= 96 <======
