Statins are used to keep cholesterol in check and are a top-selling drug in the U. S. The equation: S = 1.9x + 4.9 estimates the amount of sales, S, of statin (in billions of
dollars) 3 years after 1998.

Sales of statin in the year 2011 was billion dollars.

Sales of statin in the year
was 20.3 billion dollars.