Question

What two numbers multiply to -11 and add to 18

Answer 1

They're both irrational numbers, so they can't be written down exactly

Rounded to the nearest thousandth, they are

     18.592
and
    - 0.592  .

Just in case you actually intended to write "add to -11 and multiply to 18",
then the two numbers are

     - 9
and
     - 2 .