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

what does the below rebus means?

Find out the missing number in the picture attached:

Given that

(78)^9 = 6
And (69)^4 = 11

Can you find out

(99)^2 =?

(Note: This is Logical, not Mathematical)

I am white when I am dirty, and black when I am clean. What am I?

A blonde put eyeliner on her head. Why?

Do You See It?

Which tank will fill first?

Name a key which is hardest to turn.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?