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 = ?

Which letter of the alphabet has the most water?

What has no start, end, or centre?

John is looking at Jenifer, but Jenifer is looking at Jacob. John is married, but Jacob is not.

Is a married person looking at an unmarried person ?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

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

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

Rumel, A detective who was mere days from cracking an international smuggling ring has suddenly gone missing. While inspecting his last-known location, you find a note:

710 57735 34 5508 51 7718

Currently, there are 3 suspects: Bill, John, and Todd. Can you break the detective's code and find the criminal's name?

Who always enjoys poor health?

Today, I celebrated my 32nd birthday but I was born in 1972.
How is this possible?