Problem $7$ : Feedback Loop

The figure represents a typical control loop

$1.$ If D$($s$)=0,$ Find H$($s$)$

$2.$ If D$($s$)=$ X$($s$),$ Find H$($s$)$

$3.$ What would be H$($s$)$ if S$($s$)=1,$ for both cases?