arithmetric?

I think the question is MC question, better typing the choice.

First, find the n term.

T(n)=S(n)-S(n-1)
.....=2(n^2)+n -[2((n-1)^2)+(n-1)]
.....=2(n^2)+n-[2(n^2)-4n+2+n-1]
.....=2(n^2)+n-2(n^2)+3n-1
.....=4n-1

common difference=T(n)-T(n-1)
...........................=4n-1-[4(n-1)-1
...........................=4n-1-[4n-4-1]
...........................=4n-1-4n+5
...........................=4

Remark:
T(n) : n term
S(n): sum of the first terms