How many sides does a circle have?

I am quite hot but become too cold if you remove the first two letters. What am I?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

I start and end with 500 and carry a 5 in my heart. But I require the first letter and the first number to be complete. I am the name of a King.

Who am I ?

Alex is stranded on an island covered in forest.
One day, when the wind is blowing from the west, lightning strikes the west end of the island and sets fire to the forest. The fire is very violent, burning everything in its path, and without intervention the fire will burn the whole island, killing the man in the process.

There are cliffs around the island, so he cannot jump off.

How can the Alex survive the fire? (There are no buckets or any other means to put out the fire)

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

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

By using all numbers, i.e. 123456789 and subtraction/addition, operators number 100 can be formed in many ways.
Example: 98 + 7 + 6 - 5 - 4 - 3 + 2 - 1 = 100

But if we add a condition use of the number 32 is a must. Then there are limited solutions.
One of such solution is: 9 - 8 + 76 + 54 - 32 + 1 = 100

Can you tell me any other solution?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?