Why can't there be 1 city for 7 days

@kyleaperry because Hannah must visit 6 cities and spend at least 2 days in each city she visits. So that means 12 of the 14 days have been accounted for right off the bat. We only have 2 free days that we can add to a city Hannah visits. So the maximum number of days she can spend in one city is 4. Notice in your scenario of 1 city for 7 days, Hannah would have 5 cities remaining to visit and she needs to spend at least 2 days in each of these 5 cities, which is 10 more days. That is a total of 17 days but we only have 14 days to assign. You can also watch the video for this game setup by selecting the ▶️ icon in the top right hand corner of the screen when viewing this question. Hope this helps! Please let us know if you have any other questions.

Thank you, I missed the 6 cities part.

Did you 6*2=12 to get to the point where the 14 days have been accounted for.