The primary use of dextromethorphan is as a cough suppressant, for the temporary relief of cough caused by minor throat and bronchial irritation (such as commonly accompanies the flu and common cold), as well as those resulting from inhaled particle irritants.
As of Q4 2016, South Korea had the fastest average internet connection in the world at 26.1 Mbit/s according to the report State of the Internet published by Akamai Technologies. South Korea's speed is almost four times faster than the world average of 7.0 Mbit/s.
Usain Bolt is the fastest man on the planet. He's the world record holder in the 100 and 200 metre sprints. We can easily calculate Usain Bolt's average speed. Speed is the change in distance over time. We know how long it took him to run 100 and 200 metres, so we can work out his speed.