A concave-convex lens of refractive index \(1.5\) and the radii of curvature of its surfaces are \(30\) cm and \(20\) cm…

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:

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