3. (8 points) In the figure, the radius of the large circle is 20 cm, and the radii of the 7 small circles are all 10 cm. The area of the shaded region is $\qquad$ square centimeters ( $\pi$ is taken as 3.14).
【Solution】Solution: From the graph, we can see that the area of the shaded part $=7$ small circle areas - one large circle area
$$
\begin{array}{l}
=7 \cdot \pi \cdot 10^{2}-\pi \cdot 20^{2} \\
=300 \pi \\
=942,
\end{array}
$$

Therefore, the answer is: 942.