5. (10 points) As shown in the figure, Ruru's vegetable garden is a large rectangle composed of 4 square plots and 1 small rectangular pond. If the area of each plot is 20 square meters and the length of the garden is 9 meters, then the perimeter of the pond (the shaded part in the figure) is $\qquad$ meters.
【Solution】Solution: According to the analysis, based on the relationship between the 4 squares and the small rectangle in the figure, it is easy to know that the sum of the length and width of the pond is 9, the perimeter of the pond (the shaded part in the figure) $=2 \times 9=18$ (meters), so the answer is: 18.