Answer with explanation:
We want , (x+5) to be a Common factor of the rational expression

So, if we write
x^2+6 x+14=x²+6 x+ 5+9
So, to get (x+5) as a common factor, we should subtract 9 from the Quadratic expression.

⇒Subtract ,9 from the Numerator,That is constant term that we need in Numerator = -9