13.3 Figure 1 is formed by three identical circles touching one another, the radius of each circle is $B \mathrm{~cm}$. If the perimeter of the shaded region is $C \mathrm{~cm}$, find the value of $C$. (Take $\pi=3$ )

I3.4 Let $D$ be the integer closest to $\sqrt{C}$, find the value of $D$.
Let the centres of the circles be $P$, $Q$ and $R$ respectively.
Then $P Q=2 B=6=Q R=P R$
$\triangle P Q R$ is an equilateral $\triangle$.
$$
\begin{array}{l}
\angle P=\angle Q=\angle R=60^{\circ} \\
\text { Perimeter }=3 \times 2 \pi \times 3-3 \times \overparen{\text { MN }} \\
=18 \pi-3 \times 2 \pi \times 3 \times \frac{60}{360} \\
=15 \pi=45 \\
6=\sqrt{36}<\sqrt{45}<\sqrt{49}=7 \Rightarrow 6<D<7 \\
6.5^{2}=42.25<45 \Rightarrow 6.5<D<7, D=7 \\
\end{array}
$$

Method 2
$$
\begin{array}{l}
6=\sqrt{36}<\sqrt{45}<\sqrt{49}=7 \Rightarrow 6<D<7 \\
\because|45-36|=9,|45-49|=4
\end{array}
$$
$\therefore 45$ is closer to 49
$\therefore \sqrt{45}$ is closer to 7
$$
D=7
$$