Explain how to solve

Obtain transfer functions $C\frac{s}{R}(s)$ and $C\frac{s}{D}(s)$ of the system shown in Figure $2-23.$

Solution. From Figure $2-23$ we have

$U(s)=G_{f}R(s)+G_{c}E(s)$

$C(s)=G_p[D(s)+G_{1}U(s)]$

$E(s)=R(s)-HC(s)$