Given:- d= 30 cm f1= 15cm f2= 20cm The final image[inverted] is obtained halfway between the two lenses, v\'\'= 15 cm using the lense equation 1/f2= 1/u\'\'+ 1/v\'\' we get u\'\'= -60 cm , this is the object distance of second lens so we have the image distance of first lense as v\'= -60+30= -30 cm then applying the lense equation for first lens we get 1/f1= 1/u\'+1/v\' u\'=10cm [to the left of the first lens is the original object] Solution Given:- d= 30 cm f1= 15cm f2= 20cm The final image[inverted] is obtained halfway between the two lenses, v\'\'= 15 cm using the lense equation 1/f2= 1/u\'\'+ 1/v\'\' we get u\'\'= -60 cm , this is the object distance of second lens so we have the image distance of first lense as v\'= -60+30= -30 cm then applying the lense equation for first lens we get 1/f1= 1/u\'+1/v\' u\'=10cm [to the left of the first lens is the original object].