If we assume that the base of the container is an irregular shape with sides of 20, 5, 2, and 20
We can try to find the area of the base by completing it to form a rectangle. The area of the entire rectangle would thus be 20 times 5, or 100. Then we can substract the area of the small triangle that we have created at the bottom, which is 1/2 times base times height, or 1/2 * 20 * 3, or 30. 100 - 30 would give us 70 cm ^2.
We can then use this area of the base to find the volume of the container by multiplying by the height, which is 6 cm as given in the problem. 70 cm^2 * 6 cm = 420 cm^3, or roughly 420 cm^3 as the volume of the container.