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

A sea diver is a real show-off. He showed everyone that he can hold his breath underwater for 15 minutes.

I went to the diver and told him that I can be underwater for double the time i.e 30 minutes.
He responded that he will give me 100$ if I would be able to do it. I won 100$.

What did I do?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Using eight eights and addition only, can you make 1000?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

A man dies of old age on his 25 birthday. How is this possible?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

The day after tomorrow will be three days before Tuesday. Can you find out what is today?

Find the number of squares in the below picture

In the picture, you can see a chess board. On the top left position, the K marks a knight. Now, can you move the knight in a manner that after 63 moves, the knight has been placed at all the squares exactly once excluding the starting square?