$[6\mathrm{.}2.$b$]$ Given the following functions, what is the output?

public static int getsum$($int a$,$ int b$)1$ return $(\frac{a+b}{2})$; $\}$

public int main$()\{$

System.out.printLn $($getSum $(10,20)$;

$\}$

$15$

$10$

$30$

$25$