Which number should replace the question mark?

The dirtier I get, the whiter I look. Who am I?

Can you count the number of triangles in the given picture?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

Different lights make me strange by changing me into different sizes. What am I?

I got a bee but no honey.
got an eye but am still blind.
got a sea but no water.
got a tea but no coffee.
got a why but no answer.

What Am I?

When 99 is considered higher than 100?

Replace the question mark with the correct number below.

I have eight fingers and two thumbs but I do not live. What Am I?