Composite function rule

differentiate (2x+7) (chain rule) than you get denominator equal 2

$\dfrac{d}{dx}\dfrac{3}{4(2x+7)^9}\\ =\dfrac{3}{4}\dfrac{d}{dx}\dfrac{1}{(2x+7)^9}\\ =\dfrac{3}{4}\left(\dfrac{d}{dx}(2x+7)\right)\cdot\dfrac{-9}{(2x+7)^{10}}\\ =\dfrac{3}{4}\cdot 2\cdot -9\cdot \dfrac{1}{(2x+7)^{10}}\\ =\dfrac{-27}{2(2x+7)^{10}}$

So there u go, with a denominator equals 2.