Answer
$\color{blue}{\bf{63360x\text{ ; which is the number of inches in x miles}}}$
Work Step by Step
If $f(x)=12x$ is the number of inches in $x$ feet, and $g(x) = 5280x$ is the number of feet in $x$ miles,
$ ( f \text{ }\omicron\text{ g} )(x)= 12(5280x)$
$\color{blue}{\bf{63360x\text{ ; which is the number of inches in x miles}}}$
