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In the Digital-to-Analog converter circuit shown in the figure below, $V_{R}=10 \mathrm{~V}$ and $\mathrm{R}=10 \; \mathrm{k} \Omega$.
The voltage $V_{o}$ is
1. $-0.781 \mathrm{~V}$
2. $-1.562 \mathrm{~V}$
3. $-3.125 \mathrm{~V}$
4. $-6.250 \mathrm{~V}$