Problem Elimination of alcohol from the body

Let s have a look at an example from pharmacology - the elimination of a dmg from the body. This could be a dmg like Aspirin or Nurofen or even ethanol. In fact, the latter is probably something we all wanted to know at one point in our lives if we had 4 pints of lager in the pub, how long does it take to be under the limit for safe driving again  

Clearly this is a question that is taken from everyday life - yet it is a very good example to explain kinetics. 

Maybe we take a conservative approach and say that our metabolism requires approximately 3 hours for each pint we drink to eliminate the alcohol contained in it. How long would it take to get rid of the alcohol from 4 pints to be ok to drive again  

It should not be too difficult to find the answer to this problem the elimination rate is 3 hours per pint and we drink 4 pints, hence  

Answer After 12 hours our body should have eliminated the alcohol to a level that is safe to drive again. 

---