Answer
See below.
Work Step by Step
$S_k:3+7+11+...+(4k-1)=k(2k+1)$
$S_{k+1}:3+7+11+...+(4(k+1)-1)=(k+1)(2(k+1)+1)\\S_{k+1}:3+7+11+...+(4k+3)=(k+1)(2k+3)$
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