3. Figure 2 is a rectangle composed of 6 squares. If the area of the smallest square is 1, then the area of this rectangle is $\qquad$ .


3. 143 .

Let the side lengths of the six squares, from smallest to largest, be
$$
1, x, x, x+1, x+2, x+3 \text{.}
$$

Then, by the equality of the top and bottom sides of the rectangle, we have
$$
\begin{array}{l}
x+x+(x+1)=(x+2)+(x+3) \\
\Rightarrow x=4 .
\end{array}
$$

Thus, the length and width of the rectangle are
$$
x+x+(x+1)=13, x+(x+3)=11 \text{.}
$$

Therefore, the area of the rectangle is $13 \times 11=143$.