A student wants to compare the luminous flux of a lightbulb with that of a 1750 lumen lamp. The lightbulb ...?

Question

A student wants to compare the luminous flux of a lightbulb with that of a 1750 lumen lamp. The lightbulb and the lamp illuminate a sheet of paper equally. The 1750 lumen lamp is 1.25 meters away from the sheet of paper; the lightbulb is 1.08 meters away. What is the lightbulb's luminous flux?

Please help me with this problem.
I don't understand it.

Answer 1

Its an inverse square law thing. The intensity of the light gets spread out over a bigger area the further away you are from the source and since area of a sphere goes as 4*Pi*radius^2, intensity varies as r^2. The math is easier than the concept
1750/1.25^2 = X/1.08^2

so X = (1.08/1.25)^2 * 1750, I think