According to Newton's first law of motion, which force is expected to cause a body to accelerate? A. unbalanced force
B. balanced force
C. weak force
D. strong force

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?