B4. A rectangle is divided into eight pieces by four line segments as shown in the figure. The areas of three pieces are given, namely 3, 5, and 8.

![](https://cdn.mathpix.com/cropped/2024_04_17_4cbc91e28c87e5002633g-1.jpg?height=306&width=448&top_left_y=2234&top_left_x=810)

What is the area of the shaded quadrilateral?
B4. 16 Name the points and areas as in the figure. The area of triangle $A D F$ is equal to $a+b+e$ and also to half the area of rectangle $A B C D$. The area of triangle $C D E$ is equal to $b+c+d$ and also to half the area of rectangle $A B C D$. If we add these two areas, we get the area of the entire rectangle. Therefore, we find that

![](https://cdn.mathpix.com/cropped/2024_04_17_cb88577c1f7dc72a0c75g-2.jpg?height=343&width=503&top_left_y=180&top_left_x=1436)

$$
(a+b+e)+(b+c+d)=a+b+c+d+e+3+5+8 .
$$

By subtracting $a+b+c+d+e$ from both sides of the equation, we find $b=3+5+8=16$.