Answer:
Either
Explanation:
There are English phrases which are often used to connect the meaning of sentences, it help avoid having to repeat anther sentence to mean what is meant by the previous.
In the sentences Given;
[The flats in this tower block aren't too expensive and the flats in the tower block opposite aren't] ;
The complete statement would be ;
[The flats in this tower block aren't too expensive and the flats in the tower block opposite aren't too expensive].
However, it suffice to say ;
[The flats in this tower block aren't too expensive and the flats in the tower block opposite aren't either]
