$(4)(20$pts$)$ An op$-$amp configuration show below, please figure out the followings:

$($a$)$ Assume the op amp has infinite input resistance and zero output resistance, find the feedback factor $$;

$($b$)$ If $A={4\mathrm{.}5}^{**}{10}^4,$ find the $A_f$;

$($c$)$ What is the amount of feedback in decibels?

$($d$)$ If $|\frac{A}{A}|=25\%,|\frac{A_f}{A_f}|=?$

$($e$)$ If $F_L=50Hz$ and $F_H=120MHz,$ find $F_{Lf}$ and $F_{Hf}$;

$($f$)V_s=2(v),$ find $V_o,V_f$ and $V_i.$

R$1=15$k R$2=25$k