That's reckless driving/endangerment and usually you will go to jail. I would say that's pretty darn expensive. You may end up losing your license.
There are several Interstate Highways with a 75 MPH speed limit at various points throughout their span, but there isn't one which has that speed limit at every single point.
60
65
70
Yes it is possible. There are roadways that have a minimum speed limit, such as an interstate highway.
The speed limit on Interstate 90 in South Dakota is 80 mph or 128.7 km/h, except in city limits where the speed limit is lower, usually 55 or 65 mph.
50
scalar
As close to the posted speed limit as possible.
Whatever the speed limit for any other vehicle on that roadway is. Most of the Interstate there has a 75 MPH speed limit (except when going through cities), and you're allowed to drive 75 (provided your truck isn't governed below that).
The highest speed limit I know of on an Interstate highway in the U.S. is 75 MPH, but that varies.
The average speed limit in the United States is typically around 55-65 mph on highways and interstates, and 25-35 mph on urban roads. However, speed limits can vary greatly depending on the specific location and road conditions.