Answer:
The total number of houses are "9". The further explanation is given below.
Explanation:
The given values are:
height,
h = 28h - h²
Housing profit of developers will be:
⇒

If airport won't pay any cost for the damage,
⇒

then,
⇒
=



On putting the value of "f", we get
⇒


⇒




So that the total number of house built by the developers will be "9".