The open-loop DC gain of a unity negative feedback system

The open-loop DC gain of a unity negative feedback system with closed-loop transfer function
s + 4 is _______.
s² + 7s + 13

	C(s)	=	G(s)
	R(s)		1 + G(s) H(s)

⇒	G(s)	=	s + 4
	1 + G(s)		s² + 7s + 13

⇒	1 + G(s)	=	s² + 7s + 13
	G(s)		s + 4

⇒	1	=	s² + 6s + 9
	G(s)		s + 4

G(s) =	s + 4
	s² + 6s + 9

DC gain will occur at ω = 0

\|G\|_DC =	4
	9

	s + 4	is _______.
	s² + 7s + 13