I don't know if there's an easier way to do this but this is what I came up with. We can break this hexagon into 2 triangles and a rectangle (the 1st triangle using the top 3 points, the 2nd using the bottom 3, and the rectangle using the "middle" ones).
The relationship between the volume of a cylinder and its radius. To see that as the radius changes, the volume changes in proportion. Be able to comfortably use the volume of a cylinder formula. π is a constant and height, h, is a constant in this task.