determine the image distance for an object that is 45.0 cm from a double convex lens having a focal length of 15.0 cm

1 answer

Let the image distance be Di

1/45 + 1/Di = 1/15

1/Di = 2/45

Di = 22.5 cm

You do not need to know that the lens is double convex. All you need is the focal length.