Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

I am five letter word that is under you.
If you remove my 1st letter, then I am over you.
If you remove my 1st and 2nd letters then I am all around you.

Who am I?

What kind of tree can you carry in your hand?

Can you calculate the probability of getting a sum of six when a dice is thrown twice?

Can you find a number that lies one third of the distance between 1/3 and 2/3?

How many bricks does it take to complete a building that is 15 feet wide, 30 feet deep, and 12 feet tall made of brick?

What came first, the chicken or the egg?

Imagine a box with two cogwheels, one big with 24 teeth and one small with 8 teeth. The big one is firmly attached to the center of the box which means it does not turn or move while the small one rotates around the big one.

How many times do you think that the smaller wheel will turn compared to the box when it turns once around the big one?

What does a man do only once in his lifetime, but women do once a year after they are 29?

What has one letter and starts with an E?