Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

There’s a girl who has a large family. She has an equal amount of brothers and sisters, but each brother only has half as many brothers and sisters. What’s the correct amount of brothers and sisters?

Why is it against the law for a man living in Delhi to be buried in Mumbai?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

10+10 and 11+11 can give you the same answer.

Explain how?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

O_er_t_o_

Complete the missing letters of the given word.

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"