Answer
$0$
Work Step by Step
Substituting $s=4$ and $t=8$, the given expression, $
2s^2-t^3\div16
,$ evaluates to
\begin{array}{l}\require{cancel}
2(4)^2-(8)^3\div16
\\\\=
2(16)-512\div16
\\\\=
32-512\div16
\\\\=
32-32
\\\\=
0
.\end{array}