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Consider a closed surface $S$ surrounding a volume V. If $\vec{r}$ is the position vector of a point inside $S$, with $\hat{n}$ the unit normal on $S$, the value of the integral $\oint \oint_S 5 \vec{r} . \hat{n} d S$ is

1. $3 \mathrm{V}$
2. $5 \mathrm{V}$
3. $10 \mathrm{V}$
4. $15 \mathrm{V}$