The correct answer is 1.90 m.Concept:Lens:The transparent curved surface which is used to refract the light and make an image of any object placed in front of it is called a lens.A convex lens can converge a beam of parallel rays to a point on the other side of the lensPower of lens:It is equal to the reciprocal of the focal length of the lens/mirror in meters.Power (P) = 1/f, where f is the focal length of the lens/mirror.P = \(\frac{100}{f}\) where f is the focal length in centimeters.The unit of power of a lens is Dioptre when the focal length of the lens is taken in meters (m).The focal length of the concave lens is negative and hence its power is also negative.The focal length of the convex lens is positive and hence its power is also positive.Lens formula: \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\) where f is focal length, v is image distance and u is object distance.Explanation:For first convex lens, L1Power = \(\frac{1}{f}\)f = \(\frac{1}{p}\) = \(\frac{100}{4}\) = 25 cmGiven: Object distance, u = -50 cm, Focal length, f = 25 cm v=?\(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)\(\frac{1}{25} = \frac{1}{v} - \frac{1}{-50}\)\(\frac{1}{25} = \frac{1}{v} + \frac{1}{50}\)\(\frac{1}{25} - \frac{1}{50} = \frac{1}{v} \)\(\frac{1}{v} = \frac{2-1}{50}\)\(\frac{1}{v} = \frac{1}{50}\)v = 50 cmFor second convex lens, L2f = \(\frac{1}{p}\) = \(\frac{100}{5}\) = 20 cmObject distance, u = -80-(-50)= -80 + 50 = -30cm, focal length, f = 20cmv = ?\(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)\(\frac{1}{20} = \frac{1}{v} - \frac{1}{-30}\)\(\frac{1}{20} = \frac{1}{v} + \frac{1}{30}\) \(\frac{1}{20} - \frac{1}{30} = \frac{1}{v} \)\(\frac{1}{v} = \frac{3-2}{60} = \frac{1}{60} \)v= 60 cm Distance between original object and final image = 50 + 80 + 60 = 190 cm = 1.90 m.