The idea of these tasks is to get students to think more deeply about volume and to help visualise how different volumes “fit” together.
Questions 1-5 can be done by effectively counting cubes. Multilink cubes would be good to help with the visualisation at this point.
Question 6 is the one to get the discussion going. Is the answer 16 (if you picture them as solid cubes, rounding down) or 21.12 if you consider it as a flexible volume (e.g. a liquid)?
If you want to adapt this resource you can create your cuboids using this Geogebra resource.