Which alphabet letter is a question?

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 = ?

There is a place where if I stand up straight, I will still be considered sideways.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

What 5-letter word typed in all capital letters can be read the same upside down?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

A boy collects white seashells from the sea and brings them home every night. When he has enough of them, he decides to sell them to a trader.

The trader is ready to buy the shells and he asks the boy about the quantity. At this, the boy starts calculating. He has a giant box that contains 3 mini boxes. Two of them have another mini box inside. If the giant box can hold 50 shells, how many brown shells can he sell to the trader?

Do You See It?

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"

What has 88 keys?