The diagram above shows the floor plan for the eight apartments on the first floor where Carl and Zoë live in separate apartments. Each floor has the same floor plan. There are eight apartments on every floor. The apartments in the building are numbered from 1 to 32.
On every floor, each apartment has another apartment whose floor plan is its mirror image. For example, Apartment 8 is the mirror image of Apartment 3.
On the second floor, Apartment 9 is directly over Apartment 1, Apartment 10 is directly over Apartment 2, and so forth.
Carl lives in apartment 4. Zoë lives on the third floor in the apartment that is the mirror image of Carl's apartment.
What is Zoë's apartment number?