Answer
$4,8,12,16,....400$
$S_{100}= 20200$
Work Step by Step
Sequence: $4,8,12,16, ... 400$
$S_{100} = 4+8+12+....+400$
Sum of $n$ terms,
$S_{n}= \frac{n}{2}(a_{1}+a_{n})$
$S_{100}= \frac{100}{2}(4+400)$
$S_{100}= 50(404)$
$S_{100}= 20200$