Statins are used to keep cholesterol in check and are a top-selling drug in the U.S. The equation:

$\displaystyle {S}-{1.8}{x}={5.9}$

gives the amount of sales ($\displaystyle {S}$) of statin in billions of dollars $\displaystyle {x}$ years after 1998. According to this equation, how will/did people in the U.S. spend on statins in the year 2013?

Answer: People in the U.S. will spend billion dollars on statins in 2013.