Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

Do You See It?

Two fathers and two sons decided to go to a shop and buy some sweets upon reaching. Each of them bought 1 kg of sweet. All of them returned home after some time and found out that they had 3kg of sweets with them.

They did not eat the sweets in the way, nor threw or lose anything. Then, how can this be possible?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

During which month do people sleep the least?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

If six children and two dogs were under an umbrella, how come none of them got wet?

What will you call your mother's brother's brother-in-law?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?