A 4 kg bowling ball rolls at 8 m/s to the right and strikes a 6 kg bowling ball that is rolling at 2 m/s to the left. If the 4 kg ball bounces back with a velocity of 4 m/s to the left, what is the velocity of the 6 kg ball after the collision?

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?