#### Answer

$f'(x)=\dfrac{ad-cb}{c^2x^2+2cdx+d^2}$

#### Work Step by Step

Identify the functions in order to apply quotient rule
$h=ax+b$
$h'=a$
$g=cx+d$
$g'=c$
Apply quotient rule $(\dfrac{h}{g})'=\dfrac{h'g-hg'}{g^2}$
$f'(x)=\dfrac{a(cx+d)-c(ax+b)}{(cx+d)^2}$
$f'(x)=\dfrac{acx+ad-acx-cb}{c^2x^2+2cdx+d^2}$
$f'(x)=\dfrac{ad-cb}{c^2x^2+2cdx+d^2}$