Iwill give brainliest to whoever is correct

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?

Is the product of two rational numbers irrational or rational? first, make a hypothesis by multiplying two rational numbers. then, use variables such as x=a/b and y=c/d and the closure property of integers to prove your hypothesis.

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)