Good evening Cheryl! I am trying to decipher what they meant by external surface area, because I am not sure whether it counts the bottom surface or not. Apparently the solution that I obtained for not counting the bottom surface leads to zero height, which does not make sense.

I will next do the same question with the bottom surface counted.

The reason why I did not count the bottom surface is that in general, the model of venues (such as concert halls) are usually being stuck on a platform (like for example models of HDB flats which are placed above some material) and thus the bottom surfaces should not be counted.