At what distance from a screen will a 27 Cd lamp provide the same illumination as a 75 Cd lamp 15 m from the screen?

Q. At what distance from a screen will a 27 Cd lamp provide the same illumination as a 75 Cd lamp 15 m from the screen?

A.            9 m

B.            6 m

C.            3 m

D.            1 m

Answer: 9 m