Which number should replace the question mark?

I have a clock(12-hour format) and both the needles of the clock overlap at 12:00.
After how much time, they will overlap again?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

A maths symbol is hidden in the below Bar Graph. Can you decipher it?

A time long back, there lived a king who ruled the great kingdom of Trojan House. As a part of the renovation of the kingdom to meet future security needs, he asked his chief architect to lay down a new play in a manner that all of his 10 castles are connected through five straight walls and each wall must connect four castles together. He also asked the architect that at least one of his castles should be protected with walls. The architect could not come up with any solution that served all of King's choices, but he suggested the best plan that you can see in the picture below. Can you find a better solution to serve the king's demand?

Can you make the number 24 by utilizing the numbers 1, 3, 4 and 6? You must use one number only one time and you can use mathematical operation symbols anytime anywhere.

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time and space. What am I?

The more of this there is, the less you see. What is it?