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







Therefore,
acres of land was left unused.