The minimum sampling frequency (in samples/sec) required to reconstruct the following signal from its samples without distortion
\[ x(t)=5\left(\frac{\sin 2 \pi 1000 t}{\pi t}\right)^{3}+7\left(\frac{\sin 2 \pi 1000 t}{\pi t}\right)^{2} \]
would be
- $2 \times 10^{3}$
- $4 \times 10^{3}$
- $6 \times 10^{3}$
- $8 \times 10^{3}$