Answer- 39

Explanation-
The only non prime number

We measure 7 Minute from One Hourglass. We reverse it at 7th minute
And, 4+4=8 Minutes from Second Hourglass         –   8 Minutes
8(from 1)-7(From 2) = 1 Minute                                     –   1 Minutes
TOTAL = 9 MINUTES

EXPLANATION-
0 Minutes – Start both hourglass at the same time.
4 Minutes – The four minute glass runs out. Flip the four minute glass.
7 Minutes – The seven minute glass runs out. Flip the seven minute glass.
8 Minutes – The four minute glass runs out; the seven minute glass has been running for one minute. Flip the seven minute glass.
9 Minutes – The seven minute glass runs out.

1(s) Upon a time

Once Upon a time

Answer- 1892

It is 20th century,
and he will be x years old in x^2 year.

square(43) = 1849
square(44) = 1936 (20th Century)
square(45) =  2025

It means, in 44^44 = 1936 GRANDFATHER is of 44years old
so,
Year of birth of grandfather = 1936-44= 1892

Number of balls seen = 16,

If it is a real pyramid  then 25, But NUMBER OF BALLS I AM SURE OF(visible) is 16

It is most probably a 4 side triangular base pyramid.
So there are 25 balls.
Base: 12
2nd: 8
3rd: 4
And Top:1

The integer is -1

For Example,
Lets subtract 6 from -1.
-1 – 6 = -7
Now the successor of 6 is 7 and (-7) is exactly divisible by 7.

We can try this for any number and it will hold true.

7 Animals

Elephant
Horse
Monkey
Dog
Cat
Mouse
Snail

John can buy a item worth of 83.34 rupee.

As 15 of this is 12.5 rupee and 4.16 rupee vat.
Total 100

The number is 45

1/5 of 45 = 9
9 + 45 is 54(reverse of 45).