Answer
With
$f(x)=0.15-0.000002x$, and $g(x)=x$,
$R(x)$ can be expressed as $R(x)=f(x)\cdot g(x)$
(a product of two functions of x)
Work Step by Step
"Price per item" is a function of x items :
$f(x)=0.15-0.000002x$
"Number of items sold" is a function of x items :
$g(x)=x$
So,
$R(x)=f(x)\cdot g(x)$
$=(0.15-0.000002x)\cdot x$