Hi there!
The question is basically asking us to use a method called completing the square to 'complete' the trinomial x² + 6x + ___. To do this, we need to take half of the 'b' term, which, in this case is 6, and square it. This gives us (6/2)², giving us 9. Therefore, the answer is 9, as x² + 6x + 9 can be factored into (x + 3)². Hope this helped and have a great day!