Can you fill the blank with the correct number?

6 30 870 756030 _____

A man is found dead with a knife in his back When the investigation is done. A chair lays beside him and the forensic team finds moisture around the body.

If he committed suicide, how did he do it?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

In this image, you can see three almost identical Doraemon images. Can you spot the odd one out from them?

Why is it very easy to weigh a fish?

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?

Which digit occurred maximum times between the number 1 and 1000?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?