What is the correct function prototype for the following function?

double doSomething$($ double $x,$ int $y,$ double $z)$

$/*$ code goes here $*/$

void doSomething$()$;

double doSomething$($ double, int, double $)$;

void doSomething$($ double, int, double $)$;

double doSomething$($ double, int, char $)$