Can you fill the blank with the correct number?

6 30 870 756030 _____

John is found dead in a bare field. Nobody killed John,
John did not commit suicide.

Inspector Jacob found a bag just a few meters away from John which could save his life. What was in the bag?

The captain of a ship is telling you an interesting story and then poses a question. He says, “I have travelled the oceans far and wide. One time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly. Can you tell me how that was possible?”

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

You can win me and lose me but never buy me
You can not eat me and never want to part with me
I can make you cry or bring you joy
I am not a machine and definitely not a toy
You keep me but i am not forever just yours
You might find me in a case or on a shelf next to a vase
I am hard and i am tall if you bump me i am sure to fall
I am made of different materials and am at many events
If your lucky and fight hard I might be yours
What am I ?

What has many keys but can’t open a single lock?

I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?