What does this mathematical rebus means ?

Can you solve the maths in the below-given picture equation?

Replace the question mark in the picture below.

How do you go from 98 to 720 using just one letter?

What's the only room from which no one can enter or leave

Why is the longest human nose just 11 inches?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

By using 'because' continuously three times, can you make an English statement ?

I am a five-letter word under you,
Remove the first letter and I am above you,
Remove the second as well and I am around you.

Who am I?

How can you write nineteen in a manner that if we take out one, it becomes twenty?