9. (18 points) In the handicraft class, the teacher gives students red, yellow, and blue paper strips, with enough of each color. The teacher requires the students to place 4 paper strips in a specific order, with each subsequent strip being placed entirely on top of the already stacked strips; after placing all 4 strips, the outline viewed from top to bottom is as shown in the figure, with the colors at the 4 intersection points being red, blue, yellow, and yellow (as shown in the figure). Therefore, the number of different placement methods is
. (If at any step the color of the chosen strip is different, or the placement position is different, it counts as a different method.


12
【Solution】Solution: The yellow in the lower right corner can only be placed last,
First, place the upper left corner, there are 3 ways, then place red and blue, there are two ways, so there are $3 \times 2=6$ ways; first place the lower left corner, there are 3 ways;
First place the upper right corner, there are 3 ways;
In summary, there are $6+3+3=12$ (ways).
The answer is 12.