posted by Blegh .
A 5.00 cm tall candle is placed at a distance of 50.0 cm from a double convex lens having a focal length of 15.0 cm. What is the image distance?
Review and use the lens equation.
1/do + 1/di = 1/f
Candle height does not affect image position. Let x be the image location
1/50 + 1/x = 1/f = 1/15
1/x = 10/150 - 3/150 = 7/150
x = 150/7 = (one of your choices)