The natural frequency of the simple spring mass system

Question

1. A mass of 1 kg is suspended by means of 3 springs as shown in Figure. The spring constants K₁, K₂ and K₃, are respectively 1kN/m 3kN/m and 2 kN/m. The natural frequency of the system is approximately)      

(a) 46.90 rad/sec

(b) 52.44 rd/sec

(c) 60.55 rad/sec

(d) 77.46 rad/sec