When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

Below, you can see three complete equations and one incomplete. Based on the three complete ones, can you complete the incomplete one?

5 $ 4 $ 3 $ 9 = 4215
6 $ 9 $ 2 $ 6 = 3816
4 $ 7 $ 3 $ 3 = 1122
7 $ 2 $ 7 $ 4 = ____

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

You’ll find me on Mercury, Earth, Mars, Jupiter, Saturn, and Uranus. But never Neptune, or Venus. What am I?

Which five letter word can be added at the end of below word to form a
valid word?

> Pin
> Check
> Boiling
> View

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Why is 6 afraid of 7?

You can find some missing letters in the picture. By placing two particular letters in the spaces, you can form a nine lettered word beginning from one of the corners and going clockwise direction to the middle. Can you find out the letters and the word?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?