The answer to your problem is 6
For this case we must express the number "423" in a radical way.
We have to, we can rewrite it as:

So, we have to:

By definition of properties of powers and roots we have:
![\sqrt [n] {a ^ m} = a ^ {\frac {m} {n}}](https://tex.z-dn.net/?f=%5Csqrt%20%5Bn%5D%20%7Ba%20%5E%20m%7D%20%3D%20a%20%5E%20%7B%5Cfrac%20%7Bm%7D%20%7Bn%7D%7D)
So:

Answer:

compare the triangles ΔABC and ΔBCD
∡ABC = ∡BCD (given)
AB = CD (given)
BC = BC (common) } = > (SAS) ΔABC ≡ ΔBCD = > AC = BD
The answer you chose is correct. You should make sure that you check both of your intercepts before coming to a conclusion and determining your answer.
Hoped I helped!