What number multiplies to be 4 and adds to be -9

this makes no sense as written

Technically, any number can be multiplied by something to equal 4 and added to something to be -9. There. Problem solved.

- PM

I suspect this is meant to be "What two numbers when multiplied equal 4 and when added equal -9?"

If so, from x*y = 4 and x+y = -9, we find the two numbers to be:  (√(65) - 9)/2  and (-√(65) - 9)/2.