Find the distance between Earth and the moon if the magnitude of the gravitational force between them is1.98 × 10^20 N. The mass of Earth is 5.98 × 10^24 kg and the mass of the moon is 7.35 × 10^22 kg. The value of G is 6.67 × 10^–11 N·m^2/kg^2.

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?