3. As shown in Figure 4, all quadrilaterals are squares, and all triangles are right triangles, where the side length of the largest square is $13 \mathrm{~cm}$. Then the sum of the areas of the four shaded squares is $\qquad$
3.169.

As shown in Figure 12, by repeatedly applying the Pythagorean theorem, we get
$$
\begin{array}{l}
S_{A}+S_{B}+S_{C}+S_{D} \\
=S_{E}+S_{F}=S_{G} \\
=13^{2}=169 .
\end{array}
$$