A dockworker loading crates on a ship finds that a 20 kg crate, initially at rest on a horizontal surface, requires a 71 N horizontal force to set it...

A dockworker loading crates on a ship finds that a 20 kg crate, initially at rest on a horizontal surface, requires a 71 N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 51 N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between crate and floor.