Consider the feedback system shown in Figure $12\mathrm{.}1.$ The closed$-$loop gain is Af $=80$ and the open$-$loop gain is A $=2\backslash$times $104.($a$)$ Determine thefeedback transfer function $.($b$)$ The closed$-$loop gain is not to change by more than $0\mathrm{.}01$ percent when the open$-$loop gain changes. What is the maximum allowed change in the open$-$loop gain?