Working out the volume of a rectangular prism with unit cubes

Create a rectangular prism using the slide scales on the right.
Firstly, make a prism with the height of 1 unit cube. This is one layer.
With your partner identify the length and width of the layer. How many cubes is the volume of the prism. Explain your calculation.
Create another prism by adding a new layer onto your prism.
What can you see about the relationship between the number of layers and the number in each layer, to the volume of yours prism.
Add more layers and calculate the volume.