Answer
$S_{4}=16$
Work Step by Step
Using $S_n=\dfrac{n}{2}(2a_1+(n-1)d)$, the sum of $
1,3,5,7
$ is
\begin{array}{l}
S_{4}=\dfrac{4}{2}(2\cdot(1)+(4-1)(2))\\\\
S_{4}=2(2+6)\\\\
S_{4}=2(8)\\\\
S_{4}=16
.\end{array}
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