in the total economic impact methodology, what aspect of the model is based on the nobel prize winning work of black, merton, and scholes in finance that is commonly referred to as the black-scholes equation?

The illuminance of a surface varies inversely with the square of its distance from the light source. if the illuminance of a surface is 120 lumens per square meter when its distance from a certain light source is 6 meters, by how many meters should the distance of the surface from the source be increased to reduce its illuminance to 30 lumens per square meter?