## Algebra 2 (1st Edition)

$6n$
For an arithmetic series, the sum for the finite series is given by: $S_n=\dfrac{n(a_1+a_n)}{2}$ We know that the general formula of an arithmetic sequence is given by $a_n= a_1+(n-1) d$ Given: $6,12,18,...$ Here, $d=6$ Thus, we have $a_n=6n$