Answer:
 acres of land would be needed for 7 houses.
 acres of land would be needed for 7 houses.
 acres of land was left unused.
 acres of land was left unused.
Explanation:
We have been given that each house will be built on 5/6 of an acre. 
To find the area it will take to build 7 houses, we will multiply area need to build one house by 7 as:


 
 
Therefore, 
 acres of land would be needed for 7 houses.
 acres of land would be needed for 7 houses.
Since builder began with 10 acres of land, so we can find the unused land by subtracting 
 from 10 as:
 from 10 as:







Therefore, 
 acres of land was left unused.
 acres of land was left unused.