Replace the question mark with the correct number in the below-given picture?

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

3 6 12

4 8 16

5 10 ?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

How far can you walk into the woods?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

My cousin lives in one story house in Antarctica. His house is made the of-of sandstone. what is the color of stairs?

Jack have ten pairs of black socks, eight pairs of white socks and seven pairs of green socks. Everything is mixed in a draw. As there is no light he were not able to identify the colour of the socks. How many of the socks did he want to take to match one pair

When I asked a girl's name she told me her name is the date '07/09/2001'.

I thought for a few seconds and then I got her name. Do you?

What does the below rebus puzzle mean?