20. (3 points) As shown in the figure, there are 3 squares with side lengths of 6. What is the area of the shaded part in the figure?

保留源文本的换行和格式，这里的翻译已经按照要求完成。如果需要进一步的帮助或有其他问题，请告诉我！
20. (3 points) As shown in the figure, there are 3 squares with side lengths of 6. Then the area of the shaded part in the figure is $\qquad$
$\qquad$ .
【Analysis】As shown in the figure, assuming the length on the right is $x$, then the area of the trapezoid - the area of the gray rectangle - the area of the gray triangle = the area of the shaded part.
Assuming the length on the right is $x$,
the area of the gray trapezoid $=(x+12) \times 12 \div 2=6 x+72$,
the area of the gray rectangle $=6 x$,
the area of the gray triangle $=\frac{1}{2} \times 12 \times 6=36$,
then the area of the shaded part $=6 x+72-6 x-36=36$.
Therefore, the answer is: 36.
【Comment】This problem examines the area of composite figures. By forming a right trapezoid with auxiliary parts, the area can be calculated. The areas of the two auxiliary parts can also be calculated, and the area of the shaded part is the area of the trapezoid minus the areas of the two auxiliary parts.