What has one letter and starts with an E?

Solve the mathematical equation in the picture below.

A red house is made out of red bricks. A yellow house is made out of yellow bricks. And, a blue house is made out of blue bricks. So, what is a greenhouse made of?

Why do people go to bed?

Complete the table series riddle by finding the number that can replace "??".

There is a square piece of paper with a hole that is denoted by the circle on the top right side in the given picture. You have to cut the paper in a manner that it forms two and only two separate pieces of paper and then rearrange the pieces in a manner that the holes come in the centre of the paper.

In an Art Gallary, When the clock hit 11 am, Artist hung the painting number 30. When it struck 4 pm, he hung painting number 240 and when it struck 7:30 pm, he hung painting number 315.

Can you determine, which painting number will he hang when the time is 9:20 pm?

What has many teeth, but cannot bite?

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

The more you take me, the more you leave me behind.
Who Am I?