feet or inch
Depends entirely on your application. Use as a jump rope would be different than if being used for a computer connection.
I would measure it with a ruler.
centimeter
Any measure of length will do, but the most common would be feet or meters.
You would answer it with cubic feet
length
No. Your computer would connect directly to the cable modem via an ethernet cable.
There are many cables and components to a computer. The main cables for connecting the computer would be the power cable, and an Ethernet cable for connecting a non wireless PC to the internet.
A metres, for an approximate measure, a centimetre for a more accurate measure.
You would use meters.
I would use feet
Inches