A concave-convex lens of refractive index $$1.5$$ and the radii of curvature of its surfaces are $$30 cm$$ and $$20 cm$$, respectively. The concave surface is upwards and is filled with a liquid of refractive index $$1.3$$. The focal length of the liquid-glass combination will be

A

$$\frac{500}{11}$$ cm

B

$$\frac{800}{11}$$ cm

C

$$\frac{700}{11}$$ cm

D

$$\frac{600}{11}$$ cm