What is the word or phrase?

What do you see in the image below

The centre of the third figure is empty. What digit should fit inside?

Different lights make me strange by changing me into different sizes. What am I?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

In Greek mythology, the Sphinx sat outside of Thebes and asked this riddle of all travellers who passed by. If the traveller failed to solve the riddle, then the Sphinx killed him/her. And if the traveller answered the riddle correctly, then the Sphinx would destroy herself. The riddle:

What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?

Oedipus solved the riddle, and the Sphinx destroyed herself.

There is a square piece of paper with a hole that is denoted by the circle on the top right side in the given picture. You have to cut the paper in a manner that it forms two and only two separate pieces of paper and then rearrange the pieces in a manner that the holes come in the centre of the paper.

Can you fill the blank with the correct number?

6 30 870 756030 _____

What can you serve, but never eat?

A man in a car saw a Golden Door, Silver Door and a Bronze Door. What door did he open first?