## Intermediate Algebra (6th Edition)

$f(15)=16.8$, so diamond production is predicted to be worth 16.8 billion dollars in 2015.
We are given that the function $f(x)=.42x+10.5$, can be used to predict diamond production (where x is the number of years after 2000). To predict diamond production in 2015, we must first find x. $2015-2000=15$ years, so $x=15$. Next, we can insert x into the function. $f(15)=.42\times15+10.5=6.3+10.5=16.8$ Thus $f(15)=16.8$ tells us that diamond production is predicted to be worth 16.8 billion dollars in 2015.