R$\_($OUTI $)$ nor R$\_($OUT$2)$ R$\_($outI $)$ seen from the collector of Q$\_(2)?$ You must use small$-$signal equivalent circuit to perform this part. Show all your works.

$($b$)$ What is the effective output impedance, Rovis seen from the collector of Q$3?$ Based on knowledge acquired in part $($a$),$ you may use intuitive method to answer this part.

$4>$