An achromatic doublet of focal length 25 cm is to be made by placing a convex lens of borosilicate crown glass in contact with a diverging lens of dense flint glass. Assuming n = 1.61864, n = 1.62468, n =1-71426 and n =1-72906, calculate the focal length of each lens. Here, the unprimed and the primed quantities refer to the borosilicate crown glass and dense flint glass respectively. 15