Solution:

10

Explanation:
Equation 1 + 9 + 11 = 1 can be derived from
One (o) + nine (n) + eleven (e) = one => 1

Similarly for equation,
12 + 11 + 9
Twelve (t) + eleven (e) + nine (n) => ten (10)

Solution:

I was born in Hospital whose room number is 1950.

Solution:

Yes, by chatting,Texting or using hands(fingers signs)

Solution:

Yes, by adding 'G' to 'One'
G + One => Gone

Solution:

John Walters was drowned in the quicksand.

Solution:

No

Solution:

He cannot marry his widow's sister in any country. This is because if his wife is a widow, he is already dead.

Solution:

We believe you know that square is also a rectangle.

Solution:

This picture comprises of 31 hands and 155 fingers.

Solution:

0

Explanation:
1 * 1 * 1 = One
2 * 2 * 2 = Eight
3 * 3 * 3 = Twenty seven
4 * 4 * 4 = Sixty Four
For all the above, you can see that the first letter of the sum is the code.
Thus 5 * 5 * 5 = One twenty five

Thus 555 = O.