Answer:
40 units
Step-by-step explanation:
If two secants are drawn to a circle from one exterior point, then the product of the external segment and the total length of each secant are equal.
Thus,
[tex]AC\cdot AE=AB\cdot AD.[/tex]
Since AD=8 units, AE=6 units , EC=12+BD units, then
[tex]AC=AE+EC=6+12+BD=18+BD\ units,[/tex]
[tex]AB=AD+DB=8+BD\ units.[/tex]
Therefore,
[tex](18+BD)\cdot 6=(8+BD)\cdot 8,\\ \\108+6BD=64+8BD,\\ \\2BD=44,\\ \\BD=22\ units[/tex]
and
[tex]AC=18+22=40\ units.[/tex]