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 = ?

Replace the question mark with the number below given a simple math problem.

A blonde put eyeliner on her head. Why?

A man is found hanging dead from the ceiling of a room. The room’s dimensions are 15 x 15 x 15. The man is only 6ft tall and the rope was only 2ft long. There are no windows and only one door to the room. The door is bolted shut from the inside, and a puddle of water is under the man. How did he kill himself?

What four weights can be used to balance from 1 to 30 pounds?

A Shopkeeper collects 71 rupees in the form of 20 paisa and 25 paisa.
He collects a total of 324 coins.

Can you tell me how many number of 20-paisa and 25-paisa he got?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

Replace the question mark with the correct number in the below-given picture?

It is always ahead of me yet I can never see it. What is it?

I shave every day, but my beard stays the same. What am I?