It seems that this question is improperly worded or maybe the solution is wrong.
The question states that 15 employees donated at least $12 and 9 employees donated at least $19. This would mean, to me, that 9 out of the 15 who donated at least $12 were the people who donated $19. $19 is at least $12 after all.
I looked for errata on the book, but there were no better hits than this forum.
Thanks!