What does the below rebus riddle means?

Which number should replace the question mark?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

If 21x = 79x, what is the value of x?

What is the riddle which can be asked all day with a different correct answer each time.

A horse was tied to a rope 5 meters long and the horses food was 15 meters away from the horse. How did the horse reach the food?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?