11. (12 points) Today is December 19, we place the numbers $1 、 2 、 1 、 9$ composed of small shaded squares with a side length of 1 in an $8 \times 5$ large rectangle. When the large rectangle is rotated $180^{\circ}$, it becomes “6121”. If these two $8 \times$ 5 large rectangles are overlapped, then the number of overlapping shaded squares is $\qquad$.
【Answer】Solution: There are a total of $8 \times 5=40$ (squares);
At least one white square has $2+3+3+2=10$ (squares)
So the remaining two layers of black squares have $40-10=30$ (squares). Answer: The overlapping shaded squares total 30.

Therefore, the answer is: 30.