Answer: to determine the amount of carpet to buy for a room
Square units are units for measuring surface areas (width by length).
In this sense, the best example is:
to determine the amount of carpet to buy for a room
Because for this, you need to know the length and width of the carpet to know if it fits well in the area of the room.
The other options are incorrect, because:
-to determine the distance you ran and to determine the amount of fencing needed for your backyard refers only to measure length.
- to determine the amount of water in a pool refers only to measure volume