This is from a design entrance that I am preparing for. I know it's a little different than a theoretical projection drawing that engineering books usually cover. It is more practical and visualization based question. I have tried really hard to find some resources to understand the approach to solve this kind of questions. I didn't find any. So, if someone decides to put it on hold. I would like to request them to attach some resource in the comment.
What would be the number of surfaces of the common part?
My initial assumption was I need to first visualize the shape of the common part then count the number of surfaces. But, as people have told that is not necessary. Still, I would also like to know
How to visualize and draw the common part?
I have tried to solve this myself but the best I can come up with this. I would also like to mention that I am not an engineering student. But for my exam asks some questions from engineering drawing. I have a book for it written by someone from my country but that does not cover any union kind of question. I would be very much obliged if you show me the proper method to do it.