How to simplify Sn = 4N + n (n-1) / 2 times 6 = 3N ^ 2 + n?

How to simplify Sn = 4N + n (n-1) / 2 times 6 = 3N ^ 2 + n?

Sn=4n+n(n-1)/2x6
=4n+3n^2-3n
=3n^2+n