Solution:

In the corners of the square, tighten two ropes. Tighten another rope between them by putting rings on each rope. That rope should be tightened on the sheep's neck on the other end.

Solution:

f the last elf is taking some time to answer the question then it shall mean that the elf's before him are all wearing distinct coloured hats. However sufficient time shall be given to the last elf to give the answer.
If he views the similar coloured hats in front of him , he shall quickly tell the answer

Solution:

There can be various solutions. Here are a few that we came up with: 1 + 2 + 4/6 + 5 + 7/3 + 89 = 100
12 + 6/3 + 75 + 8/4 + 9 = 100
1/6 + 2 + 4/8 + 7/3 + 95 = 100
24 + 57 + 6/3 + 8 + 9/1 = 100
36 + 4/8 + 51 + 7/2 + 9 = 100
3/2 + 5 + 6/8 + 7/4 + 91 = 100

Solution:

I am surrounded by the enemies.

Solution:

89 (ASCII CODE OF Y)

Q W E R T Y
81 87 69 82 84 ?

Solution:

Look at the stripes at tiger's body. It's written there.

Solution:

The password that opens the chamber is 65292.

Solution:

The next number is 392.

The first number = (Square of 1 + Cube of 1)
The second number = (Square of 2 + Cube of 2)
The third number = (Square of 3 + Cube of 3)
The fourth number = (Square of 4 + Cube of 4)
The fifth number = (Square of 5 + Cube of 5)
The sixth number = (Square of 6 + Cube of 6)
Therefore, the seventh number will be
Square of 7 + Cube of 7 = 392.

Solution:

She was not able to find 11 on phone.

Solution:

The murderer is Marcus.

The notes hinted towards the name of Marcus. How?
Just take the first letter from Compound, Art Room, Restroom, Underwater Room, Study Room and Movie Room and you will get:

C, A, R, U, S and M.

Rearranging these words leads to the name Marcus who is the murderer.