Answer
$a) -3$
$b) -3$
Work Step by Step
$a)\lim _{x\rightarrow -4}\dfrac {2x^{2}+13x+20}{x+4}=\dfrac {\left( x+4\right) \left( 2x+5\right) }{x+4}=2x+5=-8+5=-3$
$b)\lim _{x\rightarrow -4}\dfrac {2x^{2}+13x+20}{x+4}=\dfrac {\dfrac {d}{dx}\left( 2x^{2}+13x+20\right) }{\dfrac {d}{dx}\left( x+4\right) }=\dfrac {4x+13}{1}=4\times \left( -4\right) +13=-3$
