A carpenter used a claw hammer to pull a 3cm nail out of a piece of wood. The nail had a resistance of 800N and the carpenter exerted a force of 40N. What was the mechanical advantage of the hammer ?

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?