(1) According to the meaning of the question, if the bottom is a rectangle, one side is 20. The centimeter is long, and the other side can be any number. The answer to this question is not unique. There are countless answers.

(2) If the bottom is a square with a side length of 20cm and a height of 30cm, there is only one answer to this question:

Trademark area =30×20×4=2400 (square centimeter)

I think this may be a mistake. I should change "the bottom is a rectangle with a side length of 20 cm" to "the bottom is a square with a side length of 20 cm."