$$
\begin{aligned}
f_{s_{1}} & =2 \times \mathrm{W}=2 \mathrm{~W} \\
f_{s_{2}} & =2 \times \mathrm{W}=2 \mathrm{~W} \\
f_{s_{3}} & =2 \times 2 \mathrm{~W}=4 \mathrm{~W} \\
f_{s_{4}} & =2 \times 3 \mathrm{~W}=2 \mathrm{~W} \\
f_{s} & =f_{s_{1}}+f_{s_{2}}+f_{s_{3}}+f_{s_{4}}
\end{aligned}
$$
For minimum bandwidth, $n=1$
$$
\begin{aligned}
R_{b} & =n f_{s} \\
R_{b} & =1 \times 14 \mathrm{~W}=14 \mathrm{~W} \\
(\text { B.W. })_{\min } & =\frac{R_{b}}{2} \\
(\text { (B.W. })_{\min } & =\frac{14 \mathrm{~W}}{2}=7 \mathrm{~W}
\end{aligned}
$$
