Can you fill the blank with the correct number?

6 30 870 756030 _____

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

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

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

A mules travels the same distance daily.
I noticed that two of his legs travels 10km and the remaining two travels 12km.
Obviously two mules legs cannot be a 2km ahead of the other 2.

The mules is perfectly normal. So how come this be true ?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

You are presented with three boxes. One of them has a red ball inside and the other two have a black ball inside each of them. You are asked to pick up the one with red ball and you pick one. Now, one of the other boxes is opened and it is found to have a black ball.

You are presented with a chance to change your box with the one that is left closed. Will you change your box? Why or why not?

How is the moon similar to a dollar?

In a football game, Christina defeated Teresa by 2 - 0 but no man from either side scored. How can this be possible?

In a guessing game, five friends had to guess the exact numbers of apples in a covered basket.
Friends guessed 22, 24, 29, 33, and 38, but none of the guesses was correct. The guesses were off by 1, 8, 6, 3, and 8 (in random order).

Can you determine the number of apples in a basket from this information?