Romeo takes a uniform 13.7-m ladder and leans it against the smooth (frictionless) wall of the Capulet residence. The ladder's mass is 23.2 kg and the bottom rests on the ground 3.43 m from the wall. When Romeo, whose mass is 70 kg, gets 88.3 percent of the way to the top, the ladder begins to slip. What is the coefficient of static friction between the ground and the ladder?