7. What is the change in gravitational potential energy for a 120.80-kg giant walking down a hill from a height of 21.23 m to 9.65 m?

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?