该图形由一个长方形内的 2 个相同的四分之一圆组成。
求阴影部分的周长。（取 $\pi = 3.14$）

1. Find the length of the top side of the rectangle

The radius of each quarter circle is $10$ cm. The top side of the rectangle is equal to the sum of the two horizontal radii at the bottom.
Length of top side $= 10 + 10 = 20$ cm

2. Find the total length of the curved arcs

The two identical quarter circles make up a semicircle. The length of the curved arcs is the circumference of a semicircle with radius $10$ cm.
Length of arcs $= \frac{1}{2} \times 2 \times \pi \times r = 3.14 \times 10 = 31.4$ cm

3. Calculate the total perimeter of the shaded part

Total perimeter $= 20 + 31.4 = 51.4$ cm