People in the U.S spend 18.8 billion dollars in 2009.
<h3>What is substituting ?</h3>
Substituting in mathematics is putting a specific value in an independent variable to observe a system.
According to the given data
Statins is the top selling drug in US to keep cholesterol in check.
The equation of the sales (S) of statin in billons of dollars x years after is
S - 1.3x = 4.5
The year difference is (2009 - 1998) = 11 years or x = 11
Putting the value of x in the given equation
S - 1.3(11) = 4.5
S = 4.5 + 14.3
S= 18.8
∴ The number of sales of statin is $18.8 billions.
Learn more about substitution here :
brainly.com/question/19516092
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