He's using the graduated cylinder method. I think the volume might be between 15 and 20. (It's kind of not obvious...)
Binomial is the correct type of polynomial for this problem
Answer:
if the area of the base is 20 then the volume is 300 if it's 16 then it's 240 but if it's 25.6 then the volume is 384. I would give you a specific answer if the area of base was specified