Question

I don't understand how he goes from the first one to the second one, can anybody help me?
(click link to see more.)

&=\frac12\left(\frac{n(n+1)(2n+1)}6+\frac{n(n+1)}2\right)\\
&=\frac1{12}\Big(n(n+1)(2n+1)+3n(n+1)\Big)\\