John has to cut some wood. First, he used a large, blunt saw and cut 3 pieces in 2 minutes. Then he used a smaller, sharper saw and cut 5 pieces in 2 minutes. Explain which saw was more efficient.

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?