Answer
$91$
Work Step by Step
Recall the explicit formula to calculate the sum of a finite arithmetic series.
$S_{n}=\dfrac{n}{2} (a_1+a_n)$
where; $a_n = n^{\text{th}} term; \\ a_1 = \ first \ term;
\\ n =\ Number \ of \ Terms ; \ \\ r =\ Common \ Ratio $
From the given quadratic series, we have:
$n=7, a_{1}=4; a_{7}=22$
Thus, substituting these values into the formula above gives:
$S_{7}=\dfrac{7}{2} (4+22) \\=\dfrac{7}{2} (26)\\=(7)(13)$
Therefore, $S_7=91$
