The 45 kv given in the problem is a typo it's supposed to be 25 kv. You can download the errata from the Kaplan website, I would recommend you do it. If I remember correctly there are several typos in the sample problems, some of which will totally change the problems.
^ and there was a thread created not to long ago that summarized the numerous errors in Kaplan. I could probably dig it up if you want. I would recommend using Kaplan sparingly, if at all. Probably does more harm than good.