How to simplify derivatives 
The math problem asks to find the derivative of the function
  $$y=(x+1)^4(x+5)^2$$

I get to the part $$(x+1)^4 \cdot 2(x+5) + (x+5)^2 \cdot 4(x+1)^3$$
How do they arrive at the answer
$$2(x+1)^3(x+5)(3x+11) ?$$

$$\begin{align}(x+1)^4 \cdot 2(x+5) + (x+5)^2 \cdot 4(x+1)^3&=(x+1)^3(x+5)\cdot\big[(x+1)2+(x+5)4\big]\\
&=(x+1)^3(x+5)\cdot\big[2x+2+4x+20 \big]\\
&=(x+1)^3(x+5)\cdot(6x+22)\\
&=(x+1)^3(x+5)\cdot 2(3x+11)\end{align}$$
