Can you fill the blank with the correct number?

6 30 870 756030 _____

John was piloting a plane behind a car but was never able to overtake it. Why?

I add 5 to 9 and get 2. The answer is correct, so what am I?

If 21x = 79x, what is the value of x?

No matter how little or how much you use me, you change me every month. What am I?

A man fell off a smuggling boat into deep water. He could not swim and he was not wearing anything to keep him afloat. It took 30 minutes for the people on the boat to realize someone was missing. The missing man was rescued two hours later on the return trip. Why didn't he drown? Note:- He didn't know swimming, the sea was deep, and He wasn't holding anything

Sherlock breaks into a crime scene. The victim is the owner who is slumped dead on a chair and have a bullet hole in his head. A gun lies on the floor and a cassette recorder is found on the table. On pressing the play button, Sherlock hears the message 'I have committed sins in my life and now I offer my soul to the great Lord' and followed a gunshot Sherlock smiles and informed the police that's its a murder.

Why did he think so?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

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

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