Chris found the derivative of $(2x + 5)^2$ as shown below.
$\frac { d } { d x }((2x + 5)^2)$ $=\frac{d}{dx}(4x^2+20x+25)=$$8x+20$

To check his solution, he tried applying the Power Rule:
$\frac{d}{dx}((2x+5)^2)=$$2(2x+5)=4x+10$

His solutions did not match! Which is the correct derivative, and why?