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 = ?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

A few friends are enjoying their sea voyage in a boat full of apples. On the way, they felt hungry and thus decided to eat the apples. Together, they ate two dozen of apples. When they have eaten the apples, will there be any change in the water level?

Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

What does this rebus riddle means ?

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

What comes
Once in a Year
Twice in a Month
4 times in a Week
6 times in a Day

Find the missing letter in the last circle logically in the given below picture.

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.