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 = ?

On a special event at the prison, 5 prisoners John, Jacob, Krist, Tang, and Dang given a chance to go to a sauna and can bring one thing with them.

Following are the things that the prisoners bring with them.
John: A soda
Jacob: Thermos
Krist: Book named "How to kill"
Tang: A Walkman
Dang: Harmonica

Since it is a Sauna, no one can see each other. After a while When the steam is switched, Tang was found dead and there was blood all around.
J Bond was called and he instantly come to know who can be the murderer. How?

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

How many times do a clock's hands overlap in a day ?

What word is represented by this rebus?

During which month do people sleep the least?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

A bomb exploded in a room full of married couples and no one died. How?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

Solve The below Equation:

ALFA + BETA + GAMA = DELTA