Tracing the Recursion. Observe the recursive solution provided below.

$1$ int fun$($int a$)$k

$2$ If $)==(0$

$3$ return $0$ ;

$4$ else

$5$ return fun $(a-1)+a$;

$63$

$7$ int main$()\{$

$8$ fun$(3)$;

$9$ return $0$ ;

$10$

a$.$ Which line$($s$)$ of this program define$($s$)$ the base case of fun$()$ method? $(5$ points$)$

b$.$ Which line$($s$)$ of this program include recursive call$($s$)?(5$ points$)$

c$.$ Trace the recursion below $($You must show the trace step by step, otherwise no credit!$)(10$ points$)$

d$.$ At what step of your recursion tracing did you hit the base case? $(5$ points$)$

e$.$ What is the final output of this code? $(5$ points$)$