The meter.
The appropriate unit is a metre.
Meters
12*sqrt(2) ----
Metres
I would use meters.
The meter.
Metres would probably be the most convenient.
Yes
21 feet
3 feet
You would typically use a measuring tape or a ruler to measure the length of a school hallway in meters, centimeters, or millimeters. If you need to measure longer distances in kilometers, you might use a measuring wheel or a GPS device.
The appropriate unit is a metre.
With a ruler, or a measuring tape.
3 feet.
3 feet.
A rule doesn't exist !