If a beam of parallel rays is incident on the lens from left, then it is focused at a distance f. On the other hand, if rays are incident from the right, then focal length is F. Ration of $\left|\frac{f}{F}\right|$  is k. Also, for an object placed at a distance 10 cm to the left of the lens a real image is formed after 1st refraction at a distance b cm to the right of the lens, for  ,$R_1=5cm$ then