public class ParaT$2023$ extends RecursiveTask $\{$

int lo$,$ hi$,$ val;

int$[]$ arr;

static final int CUT$=5$;

ParaT$2023($int$[]$ a$,$ int l$,$ int h$,$ int v$)\{$ lo$=$l; hi$=$h; arr$=$a; val$=$v;$\}$

protected Integer compute$()\{$

if$(($hi$-$lo$)<$ CUT$)\{$

int ans $=-1$;

for$($int i$=($lo$+1)$; i $<$ hi; i$++)\{$

if $($ arr$[$i$]==$val$)$ ans$=$i;

$\}$

return ans;

$\}$

else $\{$

ParaT$2023$ left $=$ new ParaT$2023($arr$,$lo$,($hi$+$lo$)/2,$val$)$;

ParaT$2023$ right$=$ new ParaT$2023($arr$,($hi$+$lo$)/2,$hi$,$val$)$;

left.fork$()$;

int rightAns $=$ right.compute$()$;

int leftAns $=$ left.join$()$;

if $($rightAns$>-1)$ return rightAns;

return leftAns;

$\}\}$

public static void main$($String$[]$ args$)$ throws Exception $\{$

int $[]$ arr $=\{0,1,2,3,4,5,0,7,8,0,10,11,12,13,14,15,0,17,18,19,20\}$;

final ForkJoinPool fjPool $=$ ForkJoinPool.commonPool$()$;

int ans $=$ fjPool.invoke$($new ParaT$2023($arr$,0,$arr.length,$0))$;

System.out.println$($ans$)$;

$\}\}//$ How would i determine the number of threads used to execute this code which is apparently $4,$ and how would i determine the output if it is $16.$