Consider the following function $fn.$

int $fn(n)\{$

if $(n==0))$

return $1$ ;

$\}$

if $(n==1)\{$

return $2$ ;

$\}$

return $2**fn(n-2)+fn(n-1)$;

$\}$

$($a$)$ Compute the value $fn(5).$ Show the steps in your computation.