What number should come in place of the question mark below?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

We can be boring,Or interesting.
We can be long,Or short.
We can have pictures,Or just words.
Many love us,But many also hate us.
What are we?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

Can you find the key in the picture below?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Two boys were admitted to a school. When the headmaster asks them about their parents, they tell him that they have same parents (father and mother). On further inquiry, it turns out that they both share the same date for their birthday.

"Are you twins," ask the headmaster.
"No," replies the boys.

Is it possible?

How can one talk without saying a single word?