Explain how surface waves can have characteristics of both longitudinal waves and transverse waves.
use 3 content related sentences. (ref: p.388-393)

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?