15*20/100 = 3.
They are applying a number of a subset of the population to the entire population. It's very misleading.
Edit: This journalist is also citing per year statistics, so take my math and multiply by 365, so that would be, "the US population smokes up to 1,095 cigarettes per person per year." The larger number implies that it is much worse. To add a little spice, I could say, "The US population smokes 1,095 cigarettes per year for every man, woman and child," which is exactly the same data set, but it's now implying that children are 1/3 of the people who smoke. Also most people don't envision a 17 year old as a child, so it further implies that young children (say 5-12) smoke.
The saddest part of this whole story is that this is what we can expect from serious journalism in this day and age. Gotta have their clicks!
Also, as an aside, take into account that there are 5+ million car accidents a year. I would guess that is or at least is one of the leading causes of chronic pain in the US.
According to the article, the 780 million pills were hydrocodone and oxycodone pills. Those are highly powerful and addictive opioids. 72 of those per inhabitant of WV per year seems insane to me.