Solution:

SIX - 9 (IX) = S
9 (IX) - 10 (X) = I
40 (XL) - 50 (L) = X

=> SIX

Solution:

Isaac Newton picks up a piece of wood and lights it from the fire on the west end of the island.

He then quickly carries it near the east end of he island and starts a new fire. The wind will cause that fire to burn out the eastern end and he can then shelter in the burnt area.

(Funny Part : Isaac Newton survives the fire, but dies of starvation, with all the food in the forest burnt )

Solution:

10

38 Sheeps = 30 ate sheeps (30 ate sounds like 38)
There's 40 Lions in a field, 30 ate Sheeps

So if you do simple maths 40 - 30 = 10
the answer is 10

Solution:

"Six" (6)

When you remove the first letter "S" from the word "Six," you are left with the letters "Ix."

"Ix" is the Roman numeral representation of the number 9.

Thus, the wordplay involves the transformation of "Six" (6) into "Ix," representing the number 9, which is an odd number in Roman numerals.

Solution:

FIVE

Which is : F(IV)E

Where IV = 4

So we achieved 4(IV) inside 5 (FIVE)

Solution:

24 Years

If you were 8 years old 8 years ago, then your current age is 8 + 8 = 16 years old.
After 8 more years pass, your age will be 16 + 8 = 24 years old.

So, you will be 24 years old in 8 years from now.

Solution:

A SINGLE WORD.

Solution:

11

You already knew the answer wasn't 26 letters. That would be too easy.
The letters in the words "the alphabet are 11

Solution:

The third Boy was in a wheelchair so he rolls out of the room instead of walking out.

Solution:

Chilwell can go through as all the person whose name contains even number of letters can go through the door.

This is a classic green glass door riddle.