## Algebra 2 (1st Edition)

$63$
We know that the general formula of an arithmetic sequence is given by $a_n= a_1+(n-1) d$ Here, $a_n=3+2(n-1)$ $a_n=2n+1$ When $n=7$, then we have $a_7=(2)(7)+1=15$ Thus, we have $S_n=\dfrac{7(3+15)}{2}=63$