Can you fill the blank with the correct number?

6 30 870 756030 _____

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

What have one eye but still cannot see?

The dirtier I get, the whiter I look. Who am I?

What is black when you buy it, red when you use it, and gray when you throw it away?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

The horse jumps over the king.
Strangely there is absolutely no scratch on him.

Can anyone explain, how is this possible?

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

As we know that white starts the game of chess. Can you find the scenario shown in the picture below is possible when all the white pieces are at the original place while the black pawn is not as in the below picture?

What has many teeth, but cannot bite?