4. (8 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 10 meters, then the perimeter of the pond in the garden (the shaded part in the figure) is $\qquad$ meters.
【Answer】Solution: According to the analysis, this figure consists of 4 small squares and one rectangle. Obviously, the sum of the length and width of the shaded part is 10, perimeter $=2 \times 10=20$ (meters). Therefore, the answer is: 20.