the first paragraph:

A real estate developer plans to build a land area of $5,000$ square meters and develop it into residential apartments consisting of $75$ units.

Construction conditions:

The developer is allowed to build only $70\%$ of the land area

The engineering consultant approved $20\%$ of the building for corridors and entrances

Maximum turns $2\mathrm{.}5$

The first question:

How much area does the building area have?

second question:

How much are the salable spaces?

The third question:

What is the average unit size?