The resonant frequency of the given series circuit is

L_eq = L₁ + L₂ + 2M = 6 H
At resonance,

ωL_eq =	1
	ωC

⇒ ω =	1	=	1
	√L_eq.C		√12

f =	1	Hz
	4 π √3

	1 Hz
	2 π√3

	1 Hz
	4 π√3

	1 Hz
	4 π√2

	1 Hz
	π √2