An automotive engine having a mass of 135 kg is supported on springs with linear characteristics. Each of the 2 front springs have stiffness of 3 $$\frac{MN}{m}$$ while the stiffness of each of 2 rear springs is 4.5 $$\frac{MN}{m}$$ The engine speed (rpm) at which resonanceis likely to occur is

A

$$\frac{10^{3}}{6 \pi}$$

B

$$\frac{1}{6 \pi}$$

C

$$\frac{10^{4}}{\pi}$$

D

$$\frac{10^{3}}{3}$$